and Their Effects on Transportation Systems: A Comprehensive Review and Their Effects on Transportation Systems: A Comprehensive Review © 2025 International Bank for Reconstruction and Development / The World Bank 1818 H Street NW Washington DC 20433 Telephone: +1-202-473-1000 Internet: www.worldbank.org SOME RIGHTS RESERVED This work is a product of the staff of The World Bank and the Global Facility for Disaster Reduction and Recovery (GFDRR). The findings, interpretations, and conclusions expressed in this work do not necessarily reflect the views of The World Bank, its Board of Executive Directors, or the governments they represent. Although the World Bank and GFDRR make reasonable efforts to ensure all the information presented in this document is correct, its accuracy and integrity cannot be guaranteed. 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All queries on rights and licenses, including subsidiary rights, should be addressed to World Bank Publications, The World Bank Group, 1818 H Street NW, Washington, DC 20433, USA; e-mail: pubrights@worldbank.org Contents v Acknowledgments vi Abbreviations 1 1. Introduction and Background 2 Areas of Concern 4 Objective and Scope of This Report 7 Thermal Comfort and Heat Measurements and Thresholds 7 Description of the Indexes Used 8 Infrastructure Measurements and Safety Thresholds 11 References 14 2. Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies 14 ROADS—Key Findings 15 Pavements under Pressure 19 Reflect, Absorb, Adapt: Cutting-Edge Techniques 20 Recommendations and Next Steps 22 TRAFFIC COLLISIONS—Key Findings 23 Rising Heat, Rising Collisions 25 Reasons behind Rising Traffic Collisions 26 Recommendations and Next Steps 27 RAILWAYS—Key Findings 28 Effect of Heatwaves on the Tracks 29 Extreme Heat Warning 30 Adapting Railways to the Heat 31 Recommendations and Next Steps 32 AIR TRANSPORTATION—Key Findings 33 Weight Restrictions Caused by Heat 35 Heat Response: Extending Runways and Rescheduling Flights 35 Recommendations and Next Steps 37 PUBLIC TRANSPORTATION—Key Findings 38 Extreme Heat and Public Transit Ridership 39 Hydration Initiatives 40 Recommendations and Next Steps ii Heatwaves and Their Effects on Transportation Systems: A Comprehensive Review 42 ACTIVE TRANSPORTATION—Key Findings 43 Heat and the Worldwide Decline in Cycling 44 Effect of Tree Canopies 45 Recommendations and Next Steps 46 References 52 3. Heatwaves and Transport User Behavior: Impacts, Consequences, and Mitigation Strategies 52 Key Findings 53 Effect of Heat on Workforce and Transport User Behavior 55 Effect of Shaded Walkways and Vegetation Islands 56 Recommendations and Next Steps 57 References 59 4. Additional Considerations 59 Key Findings 60 Prioritizing Investment 61 Regional Differences 62 Climate Inequality 62 Income 65 Interdependent Systems 67 Technological Innovations 68 References 71 5. Overarching Recommendations and Next Steps 71 Key Findings 72 Future Principles and Next Steps of Heat Resilience 77 References 79 Additional Readings 80 Appendices 80 Appendix A: Road Pavements: Impacts and Mitigation Strategies 86 Appendix B: Effects of Heat for Traffic Collision across Geographies 90 Appendix C: Railways Impacts and Mitigation Strategies 93 Appendix D: Air Transportation Impacts and Mitigation Strategies iii Contents 95 Appendix E: Public Transportation Impacts and Mitigation Strategies 99 Appendix F: Active Transportation Impacts and Mitigation Strategies 103 Appendix G: User Behavior Impacts and Mitigation Strategies Figures 4 Figure 1.1  Published Documents on Scopus Database with the Key Words Heat Waves and Transport Tables 8 Table 1.1  Overview of Thermal Comfort Measurements and Indexes Used in Heatwave Studies 9 Table 1.2  Overview of Infrastructure Temperature Measurements 10 Table 1.3  Infrastructure Safety Thresholds: Establishing and Assessing Critical 80 Table A.1  Impacts on Pavements and Corresponding Magnitude of Impacts as Identified by Multiple Studies in the Area 82 Table A.2  Structural Mitigation Strategies for Pavements 84 Table A.3  Non-Structural Mitigation Strategies for Pavements 86 Table B.1  Impacts on Pavements and Corresponding Magnitude of Impacts as Identified by Multiple Studies 90 Table C.1  Impacts of Heat on Railways and Corresponding Magnitude of Impacts as Identified by Different Studies 91 Table C.2  Mitigation Strategies for Impacts on Rail Transport Due to Heatwaves. Boxes 15 Box 2.1  Pavement’s Performance Grade 17 Box 2.2  Extreme Heat in South Africa Affecting Pavements 29 Box 2.3  Heatwave Impacts to Railways in the United Kingdom 30 Box 2.4  Stress-Free Temperature 34 Box 2.5  High Summer Temperatures Impact Airport Capacity Worldwide 55 Box 3.1   Hot Weather Impacts on Public Space Usage in Arid Algeria Photos 5 Photo 1.1  Railway Station in Lucknow, India 5 Photo 1.3  Ben-Gurian Airport, Israel 5 Photo 1.2  Expressway in Agra-Lucknow, India iv Contents Acknowledgments T his report is the result of the collaborative effort of a panel of experts convened by The World Bank, the Global Facility for Disaster Reduction and Recovery (GFDRR), and Purdue University. It was prepared by a core team led by Natalia Romero (Disaster Risk Management Specialist, World Bank), Nicholas Jones (Data Scientist, World Bank), and Paolo Avner (Senior Urban Economist, World Bank) and comprising lead author Satish V. Ukkusuri (Hubert and Audrey Kleasen Professor of Civil Engineering, Purdue University), Shagun Mittal (PhD Student, Purdue University), and Sang Ung Park (PhD Candidate, Purdue University). The work was conducted under the overall guidance of Ming Zhang (Global Director for Urban, Resilience and Land, World Bank), Nicolas Peltier-Thiberge (Global Director for Transport, World Bank), and Niels Holm-Nielsen (Head of GFDRR, World Bank). The report is based on insights developed through a literature review and through working group meetings chaired by Professor Ukkusuri and comprising the following panel members: Andrea Santos (Adjunct Professor, COPPE/Federal University of Rio de Janeiro), Arturo Ardila-Gomez (Lead Transport Economist, World Bank), Chao Ren (Professor, The University of Hong Kong), Gabriele Manoli (Assistant Professor, École Polytechnique Fédérale de Lausanne), Lee Chapman (Professor, University of Birmingham), Mikhail Chester (Professor, Arizona State University), Misha Mittal (Senior Manager, City Advisory, Expo City Dubai), and Nathalie Beauvais (Resiliency Lead for Architecture and Planning, HDR). The team benefited from valuable guidance from World Bank peer reviewers Maria Carolina Monsalve (Lead Economist), Jing Xiong (Senior Transport Economist), Mehul Jain (Senior Disaster Risk Management Specialist), and Paula Restrepo Cadavid (Lead Urban Specialist). Ana Campos-Garcia (Lead Disaster Risk Management Specialist, World Bank) provided valuable advice and Jonas Blancke (Consultant, World Bank) contributed data analysis. Editing and publication guidance was handled by Hope Steele and Erika Vargas (Senior Knowledge Management Officer), and design by Ultra Designs, Inc. Photo: MD Ashwell v Heatwaves and Their Effects on Transportation Systems: A Comprehensive Review Abbreviations °C degree Celsius °F degree Fahrenheit AC asphalt concrete AI artificial intelligence COP28 United Nations Climate Change Conference in Dubai CWR continuous welded rail HMA hot mix asphalt HVAC heating, ventilation, and air conditioning ICT information and communication technology IoT internet of things IPCC Intergovernmental Panel on Climate Change IRI international roughness index MRT mean radiant temperature MTOW maximum takeoff weight O&M operations and maintenance PCM phase change material PET physiologically equivalent temperature PG performance grade SFT stress-free temperature SUDS sustainable urban drainage systems TOWs takeoff weights UHI urban heat island UTCI universal thermal climate index UV ultraviolet Photo: MD Ashwell WBGT wet bulb globe temperature WHO World Health Organization Note: All dollar amounts are US dollars unless specified otherwise. vi Heatwaves and Their Effects on Transportation Systems: A Comprehensive Review 1 Introduction and Background C Impact of excessive heat on limate change, manifesting as increased temperatures and extreme heat events, asphalt. Photo: Bruce Kremer poses significant risks to transportation infrastructure and services globally. Asphalt pavements, steel rails, aviation networks, public transit systems, and active transportation modes face substantial pressures from heat exposure, with rippling impacts on operations, safety, user comfort, and asset maintenance cost Driven by unprecedented levels of human-induced greenhouse gas emissions, climate change presents a critical global challenge that requires immediate action to mitigate its severe impacts and safeguard the future. The recent World Health Organization’s Declaration on Climate and Health issued at the Climate Change Conference in Dubai (COP28) meeting highlighted the significance of health issues in the context of climate change along with various disasters that are occurring more frequently than before (WHO 2024). A report from the World Health Organization (WHO) highlighted that 250,000 additional deaths worldwide are expected from 2030 onward due to climate change (PAHO and WHO 2023). While extreme temperatures and heatwaves have historically occurred as a result of natural climate variability, recent evidence suggests that these events are now occurring with increased frequency, duration, and intensity—a change that is largely attributed to the impact of human-induced climate change. Although natural hazards collectively impose substantial costs on global transportation infrastructure, the risk profile varies significantly across hazard types. Flooding currently dominates these risks, with approximately $10.6 billion in expected annual damage globally; this is followed by tropical cyclones and severe storms at $0.8–$3.8 billion annually globally, while wildfires cause relatively modest direct asset losses of less than $0.5 billion globally despite significant service disruptions (Forzieri et al. 2018). However, extreme heat is rapidly emerging as a co-equal threat worldwide. Although heatwaves presently cause 1 Heatwaves and Their Effects on Transportation Systems: A Comprehensive Review relatively limited direct structural damage compared to flooding’s asset destruction, they impose substantial operational disruption costs, with over 1,000 rail speed restrictions recorded and maintenance expenses reaching €0.5 billion annually for German rail operators alone (Jaramillo et al. 2022). Critically, climate projections indicate that heat-related costs are growing at an unprecedented rate: rail buckling and pavement rutting expenses in the United States are projected to increase fivefold under the RCP 8.5 scenario compared to the RCP 4.5 scenario by 2100 and potentially exceed $300 billion annually in delay costs from track buckling repairs averaging $21,000 per event and temperature-induced pavement rutting that reduces vehicle speeds alone if unmitigated (Neumann et al. 2021). This rapid escalation stems from the fact that many transportation assets were designed for maximum temperatures of 35°C or below—thresholds that the Intergovernmental Panel on Climate Change (IPCC) warns will be routinely exceeded across mid-latitudes by 2050, long before infrastructure reaches the end of its life. Consequently, recent assessments by the IPCC, the World Bank, and the European Environment Agency have elevated extreme heat alongside flooding as a principal threat to transportation networks. Heatwaves represent the fastest- growing service-disruption hazard—one that could overtake flood losses in many mid- latitude rail and road systems under high-emissions scenarios (Espinet Alegre et al. 2019). Moreover, the cost of inaction in transportation systems is significant. Studies such as the US climate change road impacts report show that under a business-as-usual emissions scenario, annual adaptation costs for maintaining paved roads could rise from approximately $2.6 billion in 2100 (with mitigation) to nearly $10 billion without active intervention, representing over $7 billion in damages avoided through proactive policies (Murphy et al. 2023; US EPA 2015). Areas of Concern Among the areas of Among the areas of concern, the impact of increased temperature on transportation concern, the impact of infrastructure and services is a critical yet often underexplored component of disaster risk increased temperature management and climate change research. Transportation systems are the backbone of on transportation economies worldwide, facilitating the movement of people and goods. However, they are infrastructure and also highly susceptible to temperature variations. Increased temperatures can compromise services is a critical yet the integrity of infrastructure, leading to decreased service life, increased maintenance costs, often underexplored and potential safety hazards (see photo 1.1). Fifty flights were grounded in Arizona in 2017 component of disaster because of extreme heat (Kahn 2017). Without improvements to infrastructure—such as risk management and lengthened runways—this could mean 200 to 900 flights grounded annually by 2030, and climate change research. 500 to 2,200 grounded annually by 2050 (Cho 2023). Over the last 40 years, railroad buckling (or “sun kinks”) in the United States caused more than 2,100 derailments (Tang 2022). As the climate changes, heat and other extreme weather can cause equipment issues, delays, passenger discomfort, and safety risks for travelers and workers. In 2022, record-breaking temperatures to the United Kingdom, France, and Spain resulted in warped metal rails and set train tracks on fire, caused roads and runways to buckle, and heat-fueled wildfires threatened buildings and transit infrastructure (Dhanesha and Jones 2022). 2 Introduction and Background Elevated temperatures accelerate road infrastructure deterioration considerably and are expected to cause a reduction in pavement life of up to 75 percent by 2100. Adapting pavements to new conditions requires various changes in standards (for example, increases in thickness and reconstruction expenses of over $60,000 per kilometer). Rutting emerges as the primary mode of pavement failure: rut width has increased by 0.036 inches to 0.134 inches over 100 years, with a strong correlation to temperature rise. Importantly, proactive climate adaptation strategies prove far less costly than reactive approaches for pavements. Some countries are expected to exhibit a 40-fold difference in costs between proactive and reactive strategies by 2100. In railways, buckling events could cost the European Union and the United Kingdom up to €1.5 billion annually in operations and maintenance expenses by 2050 if average temperatures rise by 4°C. In Spain’s rail network, for example, the number of annual buckling incidents is projected to escalate to between 20 and 500 by the 2050s, especially in the southern and central regions of the country. Weather-related delays already account for up to 20 percent of unplanned railway delays in the United Kingdom. This percentage will likely rise with increasing temperatures. In aviation, payload capacities face a decrease of up to 6.5 percent from changing airport density metrics as temperatures rise (Coffel, Thompson, and Horton 2017). Ten to 30 percent of flights may currently face minor restrictions (Coffel, Thompson, and Horton 2017). Indirect impacts include staff and passenger comfort, altered tourism demand, and aircraft noise profiles. In public transit, usage drops once regional temperature thresholds are exceeded, especially in low-income neighborhoods. Conventional bus stops, often made of heat- retaining materials, become uncomfortably hot during heatwaves, sometimes reaching temperatures that pose the risk of skin burns. Changes in user behavior are observed. For instance, in China, a 5°C rise in temperature reduced preference for airplane and bus travel (Li et al. 2021). Additionally, in China, outdoor activities are depressed by 5–13 percent (Fan et al. 2023)​ once the temperature rises above 30°C–35°C ​​ . In India, 36 percent of metro (Jain and Singh 2021)​ users say they would change transport modes due to heat variations ​​ . Sixteen percent of Indian metro users say they would cancel trips during high temperatures​ (Jain and Singh 2021). In terms of adaptation, the use of reflective pavements, Internet of Things (IoT) sensors for railways, airport runway expansion, specialized bus stop materials, and urban greenery and corridors demonstrate tangible heat reductions of between 2.5°C and 6°C (Knott et al. 2019). Rescheduling flights and public transit to cooler times of day moderately minimizes disruptions from heat restrictions. Cooling vests for transportation staff are additional, vital measures that enhance staff comfort and safety, further underlining the importance of focusing on staff well-being in strategies to combat the effects of rising temperatures. Additionally, travel behavior incentives and warnings help users make informed decisions regarding risks and self-care. 3 Introduction and Background However, barriers exist in terms of data availability, proactive planning toolkits, financial and technological constraints, social equity gaps, and infrastructure interdependencies. Recommendations therefore emphasize improving meteorological monitoring and baseline assessment, advancing research on materials for wider temperature sustainability, integrating resilience considerations in project appraisal, developing cost-effective innovations, centering social equity across planning processes, and encouraging multisector collaboration for systemic resilience. Transportation infrastructure and services urgently require evidence-driven adaptation protocols to enhance preparedness as extreme heat events intensify worldwide. Objective and Scope of This Report This systematic literature review consolidates current knowledge and identifies research gaps regarding heat impacts across transportation asset classes. The analysis emphasizes quantifiable evidence from past studies, prioritizing data from developing regions that often bear the brunt of climate change consequences. The companion Issues Note, Preparing Resilient Transportation Systems for Heatwaves, presents a summary of the effects of heatwaves on transportation infrastructure and offers strategies for mitigation and adaptation. The objective of this review is to consolidate current knowledge (see figure 1.1) and identify knowledge gaps regarding how elevated temperatures—worsened by climate Figure 1.1 Published Documents on Scopus Database with the Key Words Heat Waves and Transport 2018 Heatwaves in Europe, US, Asia, 50 and Northern Africa + Wildfires in Sweden, Greece, and California 40 2009 United Nations Climate Change Conference in Documents per year Copenhagen (COP15) 30 20 10 0 1977 1981 1985 1989 1993 1997 2001 2005 2009 2012 2017 2021 2025 Year Source: Original figure for this publication based on data from Scopus Database. 4 Introduction and Background change—are affecting transportation infrastructure and services (photos 1.1, 1.2, and 1.3), encompassing aspects such as pavements; road safety; and rail, air, and public transportation systems as well as user behavior. In addition, based on the synthesis of literature, this report (1) identifies future considerations for weather proofing transport systems against heatwaves and (2) proposes the development of a comprehensive roadmap for transportation agencies to prepare and adapt transportation systems. The novelty of this systematic literature review is rooted in its focused examination of heatwaves and temperature rise on transportation—these are often overshadowed Photo 1.1 Railway Station in Lucknow, India Photo 1.2 Expressway in Agra-Lucknow, India Source: Kumar 2023. Source: Parashar 2020. Note: The railway tracks on the loop line melted because of heat stress at the Note: A bus with 64 people overturned after a tire burst due to high Nigohan railway station in Lucknow on June 18, 2023; a major train accident temperature causing injuries to 18 people on June 14, 2020. was averted by rerouting. Photo 1.3 Ben-Gurian Airport, Israel Source: Jerusalem Post Staff 2023. Note: Extreme heatwave caused delays with flights grounded at Ben-Gurion Airport. 5 Introduction and Background in broader climate change discussions that attempt to address all climatic factors simultaneously. Unlike existing literature that predominantly employs qualitative narratives, this report synthesizes and analyzes research that quantitatively assesses the impacts of increased temperatures due to climate change, thereby providing a clearer evaluation of its severity. While most research has traditionally concentrated on the effects of climate change on road transport infrastructure, this review expands the scope to include a diverse array of transportation systems—such as rail, air, and public transportation services, along with active transportation and user behavior—offering a holistic analysis that has been noticeably absent in prior studies. Furthermore, the geographic scope of this review is a significant departure from the existing body of work, which is largely restricted to the developed world. By including underrepresented regions such as Central Asia, Latin America and the Caribbean, the Middle East, North Africa, Sub-Saharan Africa, and South Asia, the report addresses a critical gap in the literature, acknowledging the global disparity in climate resilience and the unique challenges faced by these regions. The comprehensive approach of this review promises to yield insights that are globally inclusive and pertinent to countries that are often at the frontline of climate change impacts yet remain underexamined. This intentional inclusivity not only broadens the applicability of the review’s findings but also underscores the global interconnectedness of transportation infrastructure in the face of climate change. This report focuses This report focuses specifically on transportation within a country rather than specifically on international transport corridors, with primary emphasis on passenger transportation transportation within systems. The analysis concentrates on direct impacts of extreme heat on transport a country rather than infrastructure and users, rather than secondary or cascading effects. The transportation international transport modes examined—roads, railways, airports, public transport, and active mobility—were corridors, with primary selected based on the availability of considerable research literature documenting emphasis on passenger heatwave impacts and the prevalence of these modes in urban and national transport transportation systems. networks, particularly in low- and middle-income countries. While ports and inland waterway transport also experience significant heat-related impacts—particularly through reduced water levels, which affects navigation and cargo capacity—these modes fall outside this report’s current analytical scope. This report aims to raise awareness about the rapidly growing risks posed by extreme heat to transportation systems and to provide a foundation for adaptation planning. It focuses on synthesizing existing research and laying out strategic adaptation pathways. The beneficiaries of this review are manifold. Policy makers can use the findings to draft informed, forward-looking policies and regulations. Transportation agencies, urban planners, and development agencies can apply the insights to develop a roadmap for heat-resilient systems. The scientific community will benefit from a synthesized body of knowledge to spur further research. The public will ultimately benefit from improved safety and sustainability. While the evidence base is still evolving, this review consolidates 6 Introduction and Background currently available literature and identifies key knowledge gaps, providing a foundation for subsequent technical guidance. This report takes a deep dive into these impacts, exploring how increased temperatures due to climate change affect transportation infrastructure and services and what measures can be taken to mitigate these effects. The report draws on various studies and evidence to provide a comprehensive understanding of this critical issue. Thermal Comfort and Heat Measurements and Thresholds Various measurement systems and indexes have been developed to quantify heat stress on humans and infrastructure during extreme heat events. These standardized metrics help researchers evaluate impacts, compare findings across studies, and establish safety thresholds for transportation systems. Description of the Indexes Used Several thermal comfort indexes are used to quantify heat stress on the human body and evaluate the impacts of extreme heat events and increasing temperatures due to climate change, as shown in table 1.1. Common indexes include the Daily Maximum Temperature, the Mean Radiant Temperature (MRT), the Physiologically Equivalent Temperature (PET), the Universal Thermal Climate Index (UTCI), and the Wet Bulb Globe Temperature (WBGT). Each index has its own strengths and limitations depending on the context of the study. For example, the Daily Maximum Temperature simply measures air temperature and does not account for humidity or radiant heat sources. In contrast, PET estimates the temperature under set reference conditions that would elicit the same physiological response as the actual environment. Thus, PET provides a more realistic representation of perceived temperature. At the same time, WBGT incorporates humidity and radiant heat to specifically assess occupational heat stress thresholds. These thresholds refer to the specific limits of temperature and humidity in a workplace environment beyond which workers are at increased risk of heat-related illnesses and stress, impacting their health and productivity. Table 1.1 compares widely used thermal comfort metrics. Each measure is defined by its unique parameters, such as air temperature, radiant temperature, wind speed, humidity, and solar radiation. The table also lists key scholarly papers for each metric, illustrating their application and relevance in current research. This information underscores the need for a unified standard in measuring thermal comfort, highlighting the diversity and complexity of existing methods. Multiple indexes are valuable for different applications, but the variability in assessment metrics also poses challenges for cross-study comparisons and clearly communicating heat risk to stakeholders. Findings regarding heat exposure impacts and health risks may differ depending on the thermal comfort index applied. Thus, there have been recent calls to 7 Introduction and Background Table 1.1  Overview of Thermal Comfort Measurements and Indexes Used in Heatwave Studies PET (°C) O Meteorological Physiological Heat input model Evaporation min. 30% air temperature Wet Bulb Globe temperature 36°C Convection (Ta) 36°C min. 10% radiation (Tmrt) Radiation min. 50% humidity wind temperature humidity solar (rH, pa) Conductivity radiation cool floor less than 50% wind Clothing Heat index (Va) model Physiologically Equiv- Daily Maximum Tem- Mean Radiant Tem- Universal Thermal Wet Bulb Globe Tem- Measure alent Temperature perature perature (MRT) Climate Index (UTCI) perature (WBGT) (PET) Definition Highest temperature Combines air temperature Combines the effects of How the outdoor Empirical measure that recorded within a (radiation from sky and air temperature, mean temperature feels considers the effect of 24-hour period surroundings) and solar radiant temperature, wind (includes wind, temperature, humidity, radiation speed, and humidity temperature, humidity, wind speed, and radiation solar radiation, clothing to determine appropriate insulation, metabolic rate) exposure levels/times Literature Böcker and Thorsson Böcker and Thorsson Alattar and Indraganti Alikhanova et al. 2019; Abdel-Ghany, Al-Helal, using the 2014; Fan et al. 2023; 2014; Krüger, Minella, and 2023; Böcker and Bröde et al. 2012; Kubilay and Shady 2013; Heo, measure Heaney et al. 2019; Ngo Matzarakis 2014; Manavvi Thorsson 2014; Deevi and et al. 2021; Park, Tuller, Bell, and Lee 2019; Ohashi 2019 and Rajasekar 2020; Chundeli 2020; Dzyuban et and Jo 2014 et al. 2009; Willett and Thorsson et al. 2014 al. 2022 Sherwood 2012 Source: Original table for this publication. Note: Each measure is defined by its unique parameters—such as air temperature, radiant temperature, wind speed, humidity, and solar radiation. The table also lists key scholarly papers for each metric, illustrating their application and relevance in current research. This information underscores the need for a unified standard in measuring thermal comfort, highlighting the diversity and complexity of existing methods. determine a standardized human heat stress index for consistent reporting across climate change literature. Infrastructure Measurements and Safety Thresholds Surface transportation infrastructure can be significantly impacted by extreme heat events. Table 1.2 presents units of measurement and methodologies used by researchers to understand temperature variations in different infrastructure components. This information is crucial for infrastructure planning and management, in assessing the impacts and efficiency of various cooling and reflective technologies in urban and transportation settings. Key metrics used to quantify heat exposure risks and effects include albedo for pavement, rail temperature, and surface temperatures of sun-exposed structures such as platforms or benches. Tracking these indicators provides crucial insights into heat-related hazards and vulnerabilities. Albedo measures solar radiation reflected from paved surfaces, with higher values indicating cooler surfaces. Similarly, rail heat levels are associated with buckling risks that cause speed restrictions or cancellations. Standardized measurement of these infrastructure-specific variables supplements air temperature data in heatwave analysis. This is shown in table 1.2. Establishing high spatial resolution monitoring across transport asset types facilitates early warning and targeted adaptation interventions such as cool pavement applications, improved ventilation, and altered timetables. Furthermore, consistent documentation builds an understanding of 8 Introduction and Background Table 1.2  Overview of Infrastructure Temperature Measurements Adapted from: Xu et al. 2020 Photo: tirc83 Low Albedo High Albedo Physiologically Equivalent Measure Daily Maximum Temperature Mean Radiant Temperature (MRT) Temperature (PET) Definition Albedo Rail Temperature Surface Temperature Infrastructure Type Pavement Rail Sun-exposed surface such as a bench Definition How much sunlight is reflected by the Temperature of the steel rail (°C) Temperature of the surface directly pavement surface? (0–1) exposed to sunlight (°C) Assessment 0 = no reflection; 1 = perfect reflection Analytically assumed to be 1.5 times Measurement or heat transfer model ambient air temperature Literature using the Qin 2015 Mulholland and Feyen 2021; Sanchis et Dzyuban et al. 2022; Montero-Gutiérrez measure al. 2020 et al. 2023 Source: Original table for this publication. heat impacts on assets over time amid climate change. Overall, a coordinated emphasis on tracking albedo, rail heat, and surface temperatures advances resilience against extreme temperatures. Connecting this tangible, infrastructure-centered evidence to passenger experiences bolsters motivation for heat mitigation and planning. A comprehensive outlook on heat risks across transportation networks and users alike promotes systemic readiness for hotter, more variable summertime conditions. Table 1.3 presents a critical overview of various safety thresholds set for different types of transportation infrastructure. Exceeding these safety thresholds can lead to severe consequences, affecting the durability, performance, and safety of infrastructure components. There is a need for meticulous planning and consideration of future temperature predictions to ensure that these critical limits are not breached. The information in this table is instrumental for planners and researchers, as it encapsulates essential temperature-related parameters that determine the safety and efficacy of infrastructure under varying thermal conditions. For instance, it includes measures such as performance grade (PG) for pavements and stress-free temperature (SFT) for railway rails, each tailored to specific infrastructure types, ranging from air transport to railways. Each measure serves as a benchmark, indicating the operational limits within which these infrastructures can safely function. These measures are essential for a decision-making tool for infrastructure development and maintenance. In an era where heatwaves are becoming more intense and frequent, understanding and adhering to these safety thresholds ensures the longevity and reliability of infrastructure. There is a need for meticulous planning and consideration of future temperature predictions, emphasizing that infrastructural designs and maintenance schedules must be attuned to withstand the challenges posed by changing climate conditions. 9 Introduction and Background Table 1.3  Infrastructure Safety Thresholds: Establishing and Assessing Critical Infrastruc- Literature using the Measure Definition Example ture Type measure Pavement Pavement Grading system to classify PG 64-22 pavement is Espinet et al. 2016; Performance pavement based on expected to perform Mulholland and Feyen Grade (PG) properties and relate them adequately at 2021; Schweikert et al. Photo: mastersky to field performance at high temperatures as high 2014; Viola and Celauro and low service temperatures as 64°C and as low as 2015 –22°C Stress-Free Rails Temperature at which rails SFT in Germany is Mulholland and Feyen Temperature Photo: onuma Inthapong exhibit minimal thermal generally about 23°C 2021; Palin et al. 2013; (SFT) stress (°C) Sanchis et al. 2020 Overhead Line Railways Tension in wires set ideal at OLE Design Palin et al. 2013 Equipment this temp, ensuring proper Temperature is about Photo: Zhang mengyang (OLE) Design sag and tension (°C) 38°C in the United Temperature Kingdom Aviation Fuel Air Transport Temperature at which fuel Jet A-1 (commonly used Thompson 2016 Flash Point can vaporize enough to fuel) has a flash point ignite when exposed to an of around 38°C (100°F) Photo: Chalabala ignition source (°C) Maximum Aircraft Maximum weight at which Boeing 747-8 has a Coffel, Thompson, and Takeoff an aircraft is certified to maximum takeoff Horton 2017 Weight take off (in pounds); In hot weight of 987,000 (MTOW) Photo: Boyloso conditions, aircraft operate pounds below their usual MTOW for safe takeoff Mean Airport Air Transport Altitude above sea level at 1°C temp increase Coffel, Thompson, and Photo: Truckee Tahoe Airport Density which an airport’s air density raises the mean airport Horton 2017 Altitude is equal to the standard density altitude by atmospheric conditions approximately 100 ft 10 Introduction and Background References Abdel-Ghany, A. 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Fukao. 2009. “Evaluation of Urban Thermal Environments in Commercial and Residential Spaces in Okayama City, Japan, Using the Wet-Bulb Globe Temperature Index.” Theoretical and Applied Climatology 95: 279–89. https://doi. org/10.1007/s00704-008-0006-8 PAHO and WHO (Pan American Health Organization and World Health Organization). 2023. Climate Change and Health. https://www.paho.org/en/topics/climate-change-and-health Palin, E. J., H. E. Thornton, C. T. Mathison, R. E. McCarthy, R. T. Clark, and J. Dora. 2013. “Future Projections of Temperature-Related Climate Change Impacts on the Railway Network of Great Britain.” Climatic Change 120: 71–93. https://doi.org/10.1007/s10584-013-0810-8 Parashar, B. K. 2020. “Tyre Blowouts Have Led to Many Fatal Accidents in UP.” Hindustan Times, December 2, 2020. https://www.hindustantimes.com/cities/tyre-blowouts-have-led-to-many-fatal- accidents-in-up/story-r8ucFbQjOPW112u2Q802ZN.html 12 Introduction and Background Park, S., S. E. Tuller, and M. 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Rayner. 2014. “Mean Radiant Temperature – A Predictor of Heat Related Mortality.” Urban Climate, 10: 332–45. https://doi. org/10.1016/j.uclim.2014.01.004 US EPA (United States Environmental Protection Agency). 2015. “Climate Action Benefits: Roads.” In Climate Change in the United States: Benefits of Global Action. US EPA, Office of Atmospheric Programs. https://19january2017snapshot.epa.gov/cira/climate-action-benefits-roads_.htm l Viola, F. and C. Celauro. 2015. “Effect of Climate Change on Asphalt Binder Selection for Road Construction in Italy.” Transportation Research Part D: Transport and Environment 37: 40–47. https://doi. org/10.1016/j.trd.2015.04.012 WHO (World Health Organization). 2024. COP28 Declaration on Climate and Health. World Health Organization. https://cdn.who.int/media/docs/default-source/climate-change/cop28/cop28-uae- climate-and-health-declaration.pdf?sfvrsn=2c6eed5a_3&download=true Willett, K. M. and S. Sherwood. 2012. “Exceedance of Heat Index Thresholds for 15 Regions under a Warming Climate Using the Wet‐Bulb Globe Temperature.” International Journal of Climatology 32 (2): 161–77. http://dx.doi.org/10.1002/joc.2257 13 Introduction and Background 2 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies A dump truck is unloading fresh asphalt into a slipform ROADS—Key Findings paver, at a new road construction site. Photo: BanksPhotos. ● Elevated temperatures contribute to various detrimental effects on pavements, such as diminished stiffness and strength, increased deflections, transverse cracks, and an increased rate of asphalt deformation. Over 90 percent of damage occurs in late spring and summer. ● Adapting to projected temperature rise involves significantly increasing hot mix asphalt thickness and base layer reconstruction, costing upward of $60,000 per kilometer in some cases. ● Proactive climate adaptation strategies for pavements are much less costly than reactive approaches. Some countries are expected to exhibit a 40-fold difference in cost between proactive and reactive strategies by 2100. ● Reflective pavements that suppress surface temperatures are an effective mitigation technique, as are pavements using thermochromic materials that self- regulate temperature. ● Polymer-modified binders can withstand wider temperature ranges. But modifications add complexity and costs, requiring collaborative efforts between researchers, policy makers, and industry to develop sustainable solutions. 14 Heatwaves and Their Effects on Transportation Systems: A Comprehensive Review Pavements under Pressure One of the most significant impacts of increased temperatures on roadways is seen in pavement performance and longevity. The rise in temperatures affects pavements in several ways. Asphalt, commonly used in pavement construction, is sensitive to temperature fluctuations. Increased heat can cause asphalt to soften and deform under traffic loads, leading to rutting and compromised structural integrity. Similarly, high temperatures accelerate the aging process of asphalt, reducing its useful lifespan and increasing maintenance costs. Concrete pavements, while less heat-sensitive, are not immune to the effects of temperature: thermal expansion can lead to joint failures and cracking (Pavement Interactive 2019). Temperature fluctuations cause pavements to expand and contract, leading to cracks that can quickly expand if not repaired. Such damage is not just a minor irritation—if not addressed, it can lead to warped, uneven surfaces that present a safety hazard to both drivers and pedestrians. Extreme temperature variations can cause severe pavement damage from expansion, contraction, and—in the case of rigid pavements—slab curling. Additionally, asphalt binder rheology varies with temperature, making estimated temperature extremes and their effects a primary consideration (Knott 2020) (see box 2.1 for more information about pavement performance grading, or PG). In colder regions, roads underlaid by permafrost will be affected, with loss of structural integrity from thawing permafrost. More than 50 percent of roads in Canada fall into this category (Maadani, Shafiee, and Egorov 2021). Furthermore, greenhouse gas emissions have caused global temperatures to rise since the mid-20th century; this temperature rise is accompanied by sea-level rise. Temperature increases and sea-level rise–induced groundwater rise have been shown to cause premature pavement failure in many roadway structures (Knott 2020). BOX 2.1  Pavement’s Performance Grade Performance Grade (PG) is a grading system Temperature Grade and (2) Low-Temperature used to classify the properties of asphalt Grade. Example: PG 64-22 grade means the binders, particularly their performance in binder is expected to perform adequately for varying temperature conditions. The grades pavement temperatures between 64°C and are denoted by two numbers: (1) High- –22°C (Kennedy et al. 1994). This section discusses these impacts, exploring how increased temperatures due to climate change affect transportation infrastructure and services, particularly focusing on the effects of heat on pavements. The section draws on various studies and evidence to provide a comprehensive understanding of this critical issue. 15 Heatwaves and Transport Infrastructure: Impacts, Consequences, and Mitigation Strategies Elevated temperatures contribute to various detrimental effects on pavements. These include thermal expansion at bridge joints, diminished stiffness and strength of the asphalt layer, and notable consequences such as increased deflections, transverse cracks, and an increased rate of asphalt pavement deformation. The diminished stiffness and strength of pavements are evident in a 14 percent reduction in resilient modulus (stiffness) during winters with a 2°C temperature increase (Knott et al. 2019). A 1.8°C rise in temperature leads to up to 10 percent more cracking and a 75 percent reduction in pavement life. Notably, over 90 percent of all pavement damage occurs during the late spring and summer, while a rise of 3.5°C sees early spring contributing; at a 4.5°C higher temperature, damage extends across the entire year (Knott et al. 2019). Adapting to a projected 2.8°C temperature rise by late mid-century involves a 32 percent increase in hot mix asphalt (HMA) thickness (costing $60,000/kilometer). These costs are based on US data for overlay resurfacing on two-lane roads under typical labor and material cost assumptions. In case of base-layer failure, reconstruction is necessary ($35,000/kilometer Elevated temperatures for a 2.8°C rise), along with HMA replacement ($350,000/kilometer) (Knott et al. 2019). contribute to various HMA for pavements refers to a blend of aggregates—such as sand and gravel and asphalt detrimental effects on concrete (AC)—that is heated and mixed in specific proportions to lay down on roads, pavements. These include forming a durable, resilient road surface during construction. thermal expansion at bridge joints, diminished For flexible pavements, from 2040 to 2060, fatigue cracking is projected to rise by 2 to stiffness and strength of 11 percent, AC rutting by 9 to 45 percent, and total rutting by 5 to 34 percent; this varies the asphalt layer, and in different regions within the United States (Gudipudi, Underwood, and Zalghout 2017). notable consequences Fatigue cracking increases by 1.38 percent with a 1°C rise, while rutting increases by 2.33 such as increased percent with a 1 percent temperature rise (Gudipudi, Underwood, and Zalghout 2017). deflections, transverse Rutting, which is a top-of-pavement phenomenon, is particularly sensitive to temperature cracks, and an increased changes (Mallick et al. 2014). In rigid pavements, joint faulting increases and transverse rate of asphalt pavement cracking decreases; 1 these pavements show higher relative slab movement due to slab deformation. expansion and contraction, mitigated by low shrinkage with rising temperatures (Gudipudi, Underwood, and Zalghout 2017). Mitigation strategies include overdesigning (designing with additional structural capacity) pavement structures to counteract fatigue cracking under specific climatic conditions and forecasts (Gudipudi, Underwood, and Zalghout 2017). The International Roughness Index (IRI) is a standard metric used worldwide to assess the smoothness of road surfaces. It quantifies the roughness of a pavement, providing a numerical value that reflects the comfort and drivability of the road for vehicles. An increased IRI value has multifaceted effects that impact ride quality, fuel consumption, and road safety. Although there is a modest decrease in the time to pavement failure with an increased IRI, no significant correlation is observed between the change in time to failure due to IRI increase and temperature change. This underscores the complex interplay of factors influencing pavement performance and the importance of considering various 1 Joint faulting is vertical displacement between adjacent concrete pavement slabs, often caused by differential settlement or thermal expansion/contraction. 16 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies parameters for a comprehensive understanding of the impact of temperature rise on […] proactive adaptation pavements (see box 2.2 for an example from South Africa). strategies, which involve climate-resilient upgrades As Schweikert et al. (2014) show, proactive adaptation strategies, which involve climate- at the design stage, are resilient upgrades at the design stage, are consistently more cost-effective over the long consistently more cost- term than reactive approaches that rely solely on maintenance after damage. In developing effective over the long term countries such as Bolivia, Cameroon, and Ethiopia, a proactive adaptation scenario by 2050 than reactive approaches that incurs relatively low annual average costs of $8.4 million, $5.7 million, and $6.6 million, rely solely on maintenance respectively. However, with a reactive approach, costs escalate to $56 million, $15 million, after damage. and $50 million, respectively, representing opportunity cost increases of 165 percent, 51 percent, and 117 percent. By 2100, the opportunity costs for a no-adapt reactive approach are projected to be 604 percent, 187 percent, and 475 percent. In developed countries such as Italy, Japan, and Sweden, adopting an adaptive approach by 2050 results in annual costs of $154 million, $436 million, and $104 million. Conversely, reactive costs soar to $534 million, $1.1 billion, and $121 million. By 2100, the costs for a no-adapt reactive approach are anticipated to reach $1.3 billion, $1.7 billion, and $155 million. Across all countries, a proactive strategy proves less costly than a reactive one, with Italy exhibiting a 40-fold difference and Cameroon a 7-fold difference (Schweikert et al. 2014). The economic impacts of a 4°C temperature rise manifest in a 6.9 percent (€4.8 billion) increase in annual transportation (road and railway) operations and maintenance (O&M) costs in the European Union and the United Kingdom combined. Road-related costs BOX 2.2  Extreme Heat in South Africa Affecting Pavements ● Primary Failure Mechanisms: Permanent deformation (rutting) and fatigue cracking ● From 1980 to 2006, the maximum pavement temperature increased by up to 7°C (Mokoena et al. 2022). No Adapt scenario Annual cost = $390 million in 2090 Adapt scenario Annual cost = $65 million in 2090 ● About 34 percent additional paved roads could be achieved if the Adapt scenario is followed. ● The adaptive advantage was highest for the province of Northern Cape (Schweikert et al. 2014). Mitigation: Adding rubber crumbs or recycled plastic to bitumen instead of virgin polymers. This: ● Delays cracking, improves road fatigue properties ● Uses recycled material, is a cheaper sustainable technique Badly cracked highway in South Africa. ● Similar to the United States, Australia, and the United Kingdom Photo: EyeEm Mobile GmbH. 17 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies amount to €3.3 billion (€591/kilometer). Different road types exhibit similar percentages of road stock and share in risk. Eastern European countries such as Romania, Poland, and Bulgaria experience high rises in O&M costs, with increases of 24 percent, 33 percent, and 45 percent, respectively. Malta, however, does not face risk to pavements as the projected temperature rise aligns with current PG standards (Mulholland and Feyen 2021). Rutting emerges as the primary cause of pavement failure, exhibiting increases in rutting depth ranging from 0.036 inches to 0.134 inches for both secondary roads and interstates, with values exceeding 0.1 inches considered significant (Meagher et al. 2012). Notably, these changes demonstrate a strong correlation with temperature rise. In the case of alligator cracking,2 a temperature rise of 1.8°C over 100 years leads to an increase of less than 10 percent in the cracking (Mallick et al. 2014). This phenomenon is more severe for US interstates located in coastal areas, while secondary roads experience comparatively less severity (Meagher et al. 2012). Conversely, longitudinal cracking exhibits a decrease with temperature increase, which is attributed to low shrinkage as temperatures rise (Gudipudi, Underwood, and Zalghout 2017). This aspect suggests a nuanced relationship between temperature dynamics and different types of pavement distress, highlighting the importance of considering specific climatic influences on pavement performance. Pavement life is projected to experience a slight decrease in performance in the early- to Over the course mid-twenty-first century, followed by a pronounced, exponential decrease toward the end of a century in the of the century (Mallick et al. 2014). This rapid deterioration is particularly evident when United States, a 1.8°C temperatures regularly exceed the specified PG temperature range. Over the course of temperature increase, a century in the United States, a 1.8°C temperature increase, coupled with other climate coupled with other climate factors, has resulted in a substantial reduction in average pavement life from 16 to 4 factors, has resulted in years (Mallick et al. 2014). In Australia, a 4°C temperature rise led to a 4-year decrease in a substantial reduction pavement life (from 20 years) (Kumlai. Jitsangiam, and Pichayapan 2017). Additionally, the in average pavement life number of traffic cycles to failure will have decreased by approximately 6 million (Kumlai from 16 to 4 years (Mallick Jitsangiam, and Pichayapan 2017). Notably, when pavement failure occurs, top-down et al. 2014). fatigue cracking has a more influential role than rutting. Detailed impacts on pavements and corresponding magnitude of impacts are discussed in table A.1. For bridge infrastructure, thermal expansion generates substantial structural stresses, with prototype testing at 49°C showing 2-millimeter daily uplift and equivalent axial forces of 1,428 kilonewtons that exceed standard temperature gradient assumptions (Jaywaseelan, Russell, and Webb 2022). The differential thermal expansion between steel (12–13 microstrains per degree Celsius) and concrete (9 microstrains per degree Celsius) creates through-depth curvature that can produce tensile stresses reaching 60 percent of concrete tensile strength from solar heating alone, making composite bridges more vulnerable than all-concrete structures (Abi Shdid and El-Masri 2019; Nayeem and Billah 2025). Material degradation compounds these stresses as concrete experiences accelerated nonlinear creep above 60°C with viscosity dropping 42–65 percent (Wang 2025), 2 Alligator cracking is a pattern of interconnected cracks resembling alligator skin, typically due to fatigue failure from repeated traffic loads. 18 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies while steel prestressing strands lose over 30 percent of their yield strength and modulus at temperatures exceeding 120°C (Gales et al. 2009). Repeated thermal cycling from daily temperature fluctuations generates stress ranges of 3–5 megapascals that reduce predicted fatigue life by up to 25 percent in composite girders (Yang and You 2023), while prestressed tendons face rapid strength loss and potential buckling once temperatures exceed 260°C (Myers and Bailey 2009). Reflect, Absorb, Adapt: Cutting-Edge Techniques Mitigation efforts in pavement design involve adapting roads by selecting PG based on temperature projections (Daniel et al. 2014). Choosing asphalt binders capable of withstanding local climate variations is crucial. Additional methods to minimize the risk of road rutting include exploring alternative aggregate structures, modifiers, and pavement structures within the same PG (Mulholland and Feyen 2021). The use of asphaltic materials with harder binders proves effective in preventing rutting or cracking, especially in cases of a wide temperature range; this is achieved through the manipulation of binder properties with polymer modifiers (Dawson 2014). In terms of maintenance mitigation, frequent low-cost operations are recommended to minimize maintenance costs. Notable examples include Portugal, which conducts crack seals after 3, 6, and 12 years of road construction, resulting in significantly lower relative costs (Mulholland and Feyen 2021). Systematic annual maintenance, coupled with resealing or reconstruction at specific intervals, leads to substantial improvements in pavement life and a reduction in IRI value changes compared to relying solely on annual maintenance (Taylor and Philp 2015). Hard mitigation and adaptation strategies involve pavement cooling techniques. Reflective pavements, including both asphalt and concrete, are employed to suppress surface pavement temperatures, particularly in regions with high solar radiation. These pavements contribute to decreased temperatures throughout the day, reduced air conditioning needs, minimized smog formation, increased illumination, and enhanced durability. Thermochromic materials,3 despite their high cost, offer temperature-regulating benefits in both hot and cold conditions, though they may experience photodegradation when exposed to ultraviolet (UV) solar radiation. Evaporative pavements, especially in regions with abundant rainfall, employ porous and permeable pavers to reduce tire-road interaction, improve road safety, and decrease surface temperatures. Water-retentive pavements, with a variety of filler materials, demonstrate increased absorptivity and cooling effects (Qin 2015). Although reflective pavements effectively reduce surface temperatures, studies consistently demonstrate they can worsen pedestrian thermal comfort by increasing mean radiant temperature by 3°C–7°C and creating glare issues, as documented in field studies across 3 Thermochromic materials are temperature-sensitive coatings that reflect more heat when pavement temperatures rise, helping to reduce surface heating. 19 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies Before and after road Los Angeles, Phoenix, and Toronto that show deteriorated thermal comfort indexes despite resurfacing in Portugal. This maintenance improves safety, cooler pavement surfaces (Elmagri, Kamel, and Ozer 2024; Middel et al. 2020; Taleghani durability, and accessibility and Berardi 2018). for vehicles and pedestrians. Photo: AAlves. Techniques involving heat storage enhancement—such as phase change material (PCM)-impregnated pavements, graphite powder–filled pavements, and heat-harvesting pavements with renewable energy components—aim to regulate surface temperatures (Qin 2015). Modifications in manufacturing, including the use of polymer-modified binders for wider temperature ranges, are essential, albeit at an increased cost. Soft mitigation and adaptation strategies involve selecting temperature-susceptible materials and obtaining thematic maps for territories to guide engineers in asphalt binder selection (Viola and Celauro 2015). Understanding the statistical significance of temperature trends on pavements and fostering forums for goal deliberation are also emphasized (Viola and Celauro 2015). Explicit consideration of land use, land use planning, and non-motorized modes of transportation is crucial for holistic climate adaptation strategies (Taylor and Philp 2015). Detailed information about various mitigation strategies for impacts on pavements due to heat and increased temperature are discussed in table A.2 (structural strategies) and table A.3 (non-structural strategies). Recommendations and Next Steps Addressing the impacts of extreme heat on pavements requires strategic action in four key areas: revising standards to incorporate climate projections, investing in materials research for heat-resistant innovations, overcoming implementation barriers, and developing region-specific solutions that address both budget limitations and geographical diversity. ● Revise standards. Developing revised standards that account for the effects of increased heat from climate change on pavements has proved difficult. Integrating climate change considerations as an additional project layer exacerbates the 20 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies challenges, making overall infrastructure development more complex (McAndrews, Deakin, and Schipper 2013). ● Materials Research. More research into methods of asphalt modification to enhance overall performance and improve manufacturing processes is needed. Solutions with minimal modifications to the current manufacturing process will need to be found, along with new specifications and new testing methods for innovative materials (Viola and Celauro 2015), so that the new processes are easy to implement at large scale. The availability of accurate temperature prediction algorithms and comprehensive meteorological data is crucial but often challenging to obtain (Viola and Celauro 2015); finding ways to make those data accessible is essential. Resource constraints for project analysis pose yet another limitation, hindering thorough assessments (McAndrews, Deakin, and Schipper 2013). ● Overcome limitations. In the context of cool pavement research, limitations involve adding the costs of mitigating urban heat island (UHI) effects to the lifetime costs of pavements. Understanding how pavements influence temperature reduction throughout the day is essential. Additionally, the effects of cool pavements on UHI in buildings and pedestrians need further exploration, including looking at whether the pavement cooling effect can come at the expense of reduced comfort for pedestrians and other road users (Qin 2015). Examining the combination of evaporative pavements with reflective pavements is crucial, as is evaluating the long-term performance of cool pavements, considering factors such as reflective degradation and structural strength (Qin 2015). Contractors may face extra costs in implementing cool pavements, and there are limited policies in place to encourage the widespread deployment of such technologies. Overcoming these limitations requires establishing cross-sector working groups of researchers, policy makers, and industry stakeholders to develop effective strategies for sustainable pavement practices in the face of climate change. ● Address budget constraints and varied geography. Policy makers face budget constraints for mitigation and adaptation strategies for the long-term impacts of heatwaves on road surfaces. Moreover, mitigation and adaptation strategies cannot capture the direct impacts of heatwaves on road transport. To address these issues efficiently, geographic differences must be accounted for, and systemwide regional impacts of heatwaves first need to be clarified. It is recommended that dedicated funding for heat-related pavement mitigation and adaptation be specifically designated in city, county, and state transportation budgets. Because heatwave intensity and current road infrastructures differ worldwide, it is difficult to generalize mitigation and adaptation strategies to all regions. For example, both pavement maintenance techniques and life cycles vary across climatic zones. Therefore, an integrated, multifaceted approach is needed—one that spans regulation, infrastructure, and education to mitigate risks. Regional transportation agencies should develop localized heat-resilience plans that account for their specific climate projections, infrastructure vulnerabilities, and available resources. 21 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies Firefighters cutting the windshield on a crushed car after a traffic accident in TRAFFIC COLLISIONS—Key Findings Slovenia. Photo: vm. ● Extreme heat substantially increases traffic collision risks, with a 1–3 percent rise per 1°C increase in temperature above regional thresholds. Risks escalate more in the summer. ● Road accidents surge by 2.5 percent globally with high ambient temperatures. Specific data from developing countries such as Kuwait and Pakistan highlight temperature as a significant factor in road accidents, with notable deterioration in drivers’ performance as temperatures rise. ● Multiple intersecting factors—environmental, physiological, and psychological— contribute to the increase in crashes. ● Key reasons for this increase are heat’s effects on road conditions, on human cognition and behavior, and on driver fatigue and performance. ● Adaptation strategies involve adjusting speed limits to heat conditions, infrastructure investments for heat-resilient roads, and public awareness campaigns. ● An integrated, multifaceted approach is needed—one that spans regulation, infrastructure, and education to mitigate risks. 22 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies Evaluating the effect of extreme heat and increasing temperatures due to climate Research indicates that change on traffic collisions is crucial for several reasons. Research indicates that when when temperatures temperatures rise, so does the risk of car crashes. Higher temperatures can reduce rise, so does the risk drivers’ ability to concentrate and react to road conditions. Extreme heat can increase of car crashes. Higher driver fatigue, stress, and irritability, and reduce mental focus and reaction times. It temperatures can also causes roads and tires to soften, reducing traction. All of these are risk factors for reduce drivers’ ability to accidents. This is a direct consequence of the physiological and psychological effects concentrate and react to that extreme temperatures can have on individuals. Understanding the relationships road conditions. Extreme between temperature and accident rates and severity allows for better predictions of heat can increase driver dangerous road conditions and implementation of preventative measures before and fatigue, stress, and during heatwaves. When roads and transport systems are built or upgraded, designing irritability, and reduce for projected higher temperatures can improve safety. This includes choice of materials, mental focus and reaction drainage, signage, speed limits, and so on. times. It also causes roads and tires to soften, Evaluations allow for the identification of effective mitigation policies regarding speed reducing traction. limits, travel times/modes, warning systems, vehicle maintenance, and so on. This allows both drivers and officials to be better prepared. Mitigation strategies can be diverse: they can include ensuring the proper functioning of air conditioning in vehicles, parking in cool or shaded areas (and ensuring that cool or shaded areas to park are available), and avoiding driving barefoot, which can compromise a driver’s ability to operate the vehicle. More broadly, strategies also involve mainstreaming climate change adaptation into urban strategies and transportation planning, which is crucial for ensuring safer mobility in the context of a changing climate. Rising Heat, Rising Collisions The correlation between increasing temperatures due to climate change and traffic collisions is a critical area of research, demonstrating significant regional and demographic variations. Road accidents surge by 2.5 percent globally with high ambient temperatures (Liang et al. 2022). Studies employing statistical and econometric modeling have yielded insights into this relationship across different geographies. In the continental United States, for instance, there is a 2.9 percent increase in collision risk on heatwave days (Wu, Zaitchik, and Gohle 2018). This risk escalates for specific demographics, such as drivers aged 56–65 years (8.2 percent) and those driving on rural roadways (6.1 percent). Both male and female drivers show a positive association with increased accident risks during high temperatures (Wu, Zaitchik, and Gohle. 2018). In New York, the accident risk rises by 1.58 percent over two days for every 1°C increase in mean daily temperature above 26.1°C (Hou et al. 2022). Similarly, in Indiana, accidents on interstate highways correlate positively with summer temperatures (Rosselló and Saenz-de-Miera 2011). Alabama reports a substantial 23.5 percent increase in accidents on heatwave days without precipitation, with variations noted across different driver demographics and vehicle- or road-related factors (Wu 2022). European analyses present comparable results—a 1°C to 2°C rise relates to a 1–2 percent jump in road accidents. Collision risks escalated more on motorways by 2–3 percent in France and the Netherlands, and in rural roads in Netherlands by 1 percent. Urban roads 23 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies also faced risks but these were lower, at 0.4 percent in France (Bergel-Hayat et al. 2013). Southern Europe faced similar threats—a 5 percent higher crash rate on days above 30°C was seen in Athens, Greece (Bergel-Hayat et al. 2013). In Spain’s Catalonia region, crash risks rose 2.9 percent per degree Celsius during heatwaves while performance- related collisions grew 1.1 percent. The Balearic Islands in Spain proved an exception with insignificant correlations (Basagaña et al. 2015). Asian countries also report a positive correlation between temperature and traffic accidents. In Shenzhen, China, a 1°C increase above 17°C leads to a 0.9 percent rise in hourly road casualties, with greater effects during warm seasons and peak hours (Zhan et al. 2020). Taipei City, Taiwan, China, shows a 0.8 percent increase in accidents for each degree increase in temperature (Lin et al. 2015), while Macao SAR, China, reports an increase in mild injuries with temperature rises (Lio et al. 2019). Kuwait (Al-Harbi, Yassin, and Bin Shams 2012) and Pakistan (Ali, Yaseen, and Khan 2020) highlight temperature as a significant factor in road accidents, with a notable deterioration in drivers’ performance as temperatures rise. However, in regions such as Africa (Milford et al. 2016) and the Nordic countries (Fridstrøm et al. 1995), the impact of temperature on road collisions is less significant, possibly because of already high baseline temperatures or different daylight patterns. Detailed impacts on traffic collision and corresponding magnitude of Impacts are discussed in table B.1. The message is clear: climate change and associated extreme heat critically impact global road safety. This evidence underscores the impact of climate change, particularly rising A crashed truck on the ditch temperatures, on road safety. It highlights the heightened vulnerability of developing on a regional highway in Rajasthan, India. Photo: and high-income countries with hot climates and emphasizes the need for targeted Salvador-Aznar. interventions that consider demographics, seasonality, road types, and times of day. 24 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies Reasons behind Rising Traffic Collisions The increase in traffic collisions due to extreme heat and rising temperatures can be attributed to a confluence of environmental, physiological, and behavioral factors. These three factors are described below. ● Environmental factors and road conditions. Temperature changes significantly affect environmental conditions such as humidity, which can cloud vehicle windows and windscreens, thereby reducing visibility (Al-Harbi, Yassin, and Bin Shams 2012). High road surface temperatures contribute to vehicle breakdowns, such as flat tires, and adversely affect road infrastructure (Shanks, Ansari, and Ai-Kalai 1994). Roads may soften or buckle under extreme heat, leading to asphalt scouring or outflow (Vajda et al. 2014). High temperatures can also cause roads to swell, creating ruts and potholes, and exert increased pressure on bridge joints, especially in high-traffic areas (Melillo, Richmond, and Yohe 2014). These deteriorating road conditions substantially elevate the risk of collisions. ● Physiological and psychological effects on humans. Human work capacity notably declines in high-temperature environments, increasing the risk of accidents (Basagaña et al. 2015). People in hot conditions are prone to making more technical errors, drifting out of lanes, making larger steering adjustments, missing signals, and Blinding sun on a highway in experiencing heightened fatigue. They become more irritable and drowsier, leading to Spain. Photo: mtreasure. lower overall driving performance (Daanen, van de Vliert, and Huang 2003). Heatwaves can disrupt sleeping patterns, causing increased tiredness among drivers (Hermans et al. 2006). There is a notable trend of falling asleep while driving being more common in summer than in winter (Lan, Wargocki, and Lian 2011). Additionally, sun glare elevates collision risk, particularly at high speed limits (Becker, Rust, and Ulbrich 2022). Such physiological and psychological impacts significantly impair driving abilities, raising the likelihood of traffic incidents. ● Behavioral responses to heat. In response to high temperatures, drivers often alter their driving patterns. Many prefer to shift their planned trips to cooler times of the day, such as late evening or early morning (Hermans et al. 2006). However, this shift in timing does not necessarily mitigate the risks associated with heat-induced fatigue and reduced cognitive performance. Age differences play a crucial role: drivers of different ages have different levels of cognitive competency, reaction speed, driving experience, and experience in handling dangerous situations. Younger drivers may exhibit more aggressive and dangerous driving habits in response to heat stress (Park, Choi, and Chay 2021). In summary, the reasons behind the increase in traffic collisions due to extreme heat and temperature rise are multifaceted, encompassing environmental, physiological, and behavioral dimensions. This complex interplay highlights the need for comprehensive strategies to mitigate these risks and adapt to the evolving challenges posed by climate change. Holistic mitigation policies are vital to reverse the pattern. 25 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies Recommendations and Next Steps Mitigating the increase in traffic collisions due to extreme heat and rising temperatures, a challenge exacerbated by climate change, will require a multifaceted approach. The strategies must address both the immediate effects of heat on drivers and vehicles as well as the longer-term impact on road infrastructure. A few promising approaches are: ● Adapt speed limit criteria. By adjusting speed limits to consider the temperature, authorities can proactively reduce the risk of accidents that are more likely under heat stress conditions. Lowering speed limits in extreme heat can compensate for reduced driver reaction times and potential vehicle malfunctions, thereby enhancing road safety. Enable targeted interventions by installing heat-warning signage and temporarily reducing speed limits only in high-risk corridors during extreme heat events. ● Invest in road infrastructure. Road infrastructure investments are negatively associated with heat-related road injuries. Investing in road infrastructure that is resilient to high temperatures can significantly mitigate the risk of accidents. Improvements could include using heat-resistant materials in road construction, enhancing drainage systems to cope with thermal expansion, and reinforcing critical infrastructure such as bridges and overpasses. Well-constructed and maintained roads are particularly crucial for long trips, where the likelihood of fatigue-induced accidents is higher. Ensuring that road surfaces remain intact and free from heat-induced damage such as buckling or pothole formation is vital for maintaining safe driving conditions. ● Implement additional mitigation measures. Beyond these primary strategies, public awareness campaigns about the risks of driving in extreme heat are important. These campaigns may focus on the signs of heat exhaustion and the importance of staying hydrated. Providing more shaded parking areas and rest stops along highways can give drivers opportunities to cool down and rest, especially during long journeys. Enhanced weather forecasting and real-time alerts about heatwave conditions can help drivers make informed decisions about their travel plans. ● Support transport design. Beyond roads, larger transport design also warrants an evolution. Warming raises risks for groups such as motorcyclists in Asian nations. Improved motorcycle lane infrastructure and protective gear decrease the number of motorcycle accidents. In conclusion, mitigating the increase in traffic collisions due to extreme heat and temperature rise requires an integrated approach that combines adjustments to driving regulations, substantial investments in road infrastructure, and widespread public education. As climate change continues to elevate temperature extremes, these strategies become increasingly crucial for maintaining road safety. 26 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies A local suburban commuter train in the countryside near RAILWAYS—Key Findings Pune, India. Photo: Dinesh Hukmani ● Rising temperatures could lead to an additional €1.5 billion in annual railway operations and maintenance (O&M) expenses in the European Union and United Kingdom if temperatures rise by 4°C. In Germany alone, a 4°C temperature rise could result in an annual cost of €882 million. ● In Spain, annual buckling events on railway tracks are projected to increase to between 20 and 500 by the 2050s, especially in the south and center of the country. ● In the southern United Kingdom, heat stress episodes for railway staff could increase 3 to 8 times by the 2040s. ● Weather-related delays already account for up to 20 percent of unplanned railway delays in the United Kingdom. This percentage could rise with increasing temperatures. ● Internet of Things (IoT) sensors and devices for monitoring rail defects are seen as having the greatest initial impact of the various temperature mitigation strategies. Their development and implementation are crucial for providing early warnings about extreme temperatures. ● There is a lack of established methodology to prevent sun kink deformations and a need for research into innovative materials, localized speed management protocols, and cost-benefit analyses for track design alterations. Investment in advanced sensor technology is critical for mitigating thermal damage to railways. 27 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies This section considers the impacts of increased temperature on railway infrastructure and services, as well as the challenges posed by climate change and the mitigation strategies being employed to combat these impacts. Climate-driven extreme weather poses serious challenges for railway infrastructure. Heatwaves can cause tracks to buckle and expand, inviting train derailments, while freezes can damage overhead power lines. Rising temperatures can lead to a range of detrimental effects on railway infrastructure, operations, users, and staff. Asphalt railbeds can soften and buckle under intense heat, causing track distortions and posing safety hazards. Extreme heat events can also cause thermal expansion of steel rails, leading to buckling and potential derailments. The trains run on reduced schedules, and even with speed restrictions there is fear that the aging rail networks could fail in the extreme temperatures (Foerster 2022). Weather-related delays already account for up to 20 percent of unplanned railway delays in the United Kingdom (box 2.3). This percentage could rise with increasing temperatures (McAndrews, Deakin, and Schipper 2013). Sun kinks are a type of track distortion or buckling in railways that occur due to excessive heat (Chinowsky et al. 2019). They occur when the temperature rises significantly, causing the metal rails to expand beyond their capacity to be absorbed by the track structure and leading to a sudden misalignment or warping of the rail track, creating a kink. These pose significant safety risks as they can derail trains or cause accidents, especially when trains are traveling at high speeds. However, mitigation strategies are being developed to combat these impacts. For example, the German national railway company Deutsche Bahn has implemented several measures to adapt its network to climate change (Deutsche Bahn 2021). These measures include using heat-resistant materials for track construction, installing drainage systems to prevent flooding, and developing a climate risk management plan. Effect of Heatwaves on the Tracks Rising temperatures pose significant challenges for railway systems, with a multitude of impacts. Rail buckling and sun kinks can occur, leading to misalignments, particularly in low curvature lines. Overhead line equipment can sag beyond the design temperature range of –18°C to 38°C, potentially causing loss of contact with the pantograph (Palin et al. 2013). Maintenance becomes more difficult, as ballast work is not advised in high heat, and increased temperatures lead to higher operations and maintenance (O&M) costs (Palin et al. 2013). In the European Union and the United Kingdom, a 4°C rise could result in an additional €1.5 billion in annual railway O&M expenses. Germany could face an annual cost of €882 million with such a temperature increase (Mulholland and Feyen 2021). Speed restrictions, which are used to mitigate these issues, might paradoxically contribute to further buckling (Chinowsky et al. 2019). This is because slower-moving trains exert force to the same section of a track for a longer duration than fast-moving trains, heating the rails even more because of the friction and sustained pressure. Additionally, slower train speeds may lead to increased rail traffic congestion, exacerbating buckling. Deploying 28 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies BOX 2.3 sensors Heatwave targetedto forImpacts Railways speed in the United restrictions Kingdom could be more cost-effective, with proactive strategies estimated to cost between $4 billion and $29 billion by the end of the century, Extreme compared Heat Warning to $103 billion to $138 billion for reactive ● Network measures Rail issued a notice (Chinowsky et al.that users 2019). without essential trips could cancel their ● A red extreme heat warning was issued in trips without penalty and possibly with a the United Kingdom in 2022. refund during the cancellation period. ● Rails absorb more than 68°F (20°C). Traveling users should wear cool clothes. Railways eventsand can expand are bend, flex and— ● In Spain, buckling projected to increase to between 20 and 500 annually by Railway temperatures were promptly in serious cases— buckle. ● the 2050s, particularly in the south and center of the country (Sanchis et al. 2020). In the monitored. ● Overhead southern Unitedpower lines—especially Kingdom, older buckling conditions could occur over 30 percent of the summer The rails were painted white on extreme ones—can also expand and sag in hot a doubling ● months by the 2040s, with Scotland seeing of such incidents. In terms of track heat sections to reflect the heat impacts. weather, so maintenance, thetraveling number more slowly reduces of non-workdays for track workers due to high temperatures couldthe damage. risk ofor double even triple in parts of the United Kingdom by the 2040s (Palin et al. 2013). ● Travel times increased more than usual Recommendations during this heat warning. ● Policy makers should consider the trade- ● In Britain’s 20 busiest stations, the offs between the execution of the speed number of passengers dropped by about restriction and the passengers’ increased Additional impacts include increased heat stress on staff, with the southern United 20 percent in July 2022 compared to travel time and health conditions. Kingdom anticipating three to eight times more heat stress episodes in the 2040s usual (Network Rail Limited 2022). ● Policy makers should consider seamless (Palin et al. 2013). Mitigation measures such as using enhanced vegetation to stabilize monitoring of rails based on IoT-based A Southeastern train passes embankments, phasing out old train stock for trains with better air conditioning, and Mitigation sensors for railways as well as more through heat haze in Ashford, cleaning tracks more frequently to address leaf fall and vegetation growth are being Kent as the UK has surpassed localized mitigation efforts. ● Train speeds considered. were limited Moreover, to 90 miles ventilation issuesperin underground railway systems are exacerbated the hottest July day on record. Photo: Gareth Fuller. hour, during down high heatfrom 100 or 125 episodes, miles with per hour. station temperatures potentially reaching 11°C above the 29 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies comfortable ambient range of 17°C–25°C (Baker et al. 2010). Detailed impacts on railways and corresponding magnitude of impacts are discussed in table C.1. Adapting Railways to the Heat To mitigate the impacts of temperature rise on railways, several strategies are being considered or implemented. Adjusting the stress-free temperature (SFT) is one approach, with suggestions to apply higher SFT limits nationwide or to set regional SFTs that reflect projected future temperatures, as seen in Australia and the United States (Palin et al. 2013) (see box 2.4 for more information about SFT). However, a higher SFT carries the risk of rail cracking or breaking at lower temperatures (Palin et al. 2013). In high-temperature periods, reducing train speeds can help, although it may paradoxically increase the risk of buckling and contribute to delays (Chinowsky et al. 2019). Weather-related issues already account for up to 20 percent of unplanned delays in the United Kingdom (Thomas, Jaarsma, and Tutert 2013). BOX 2.4 Stress-Free Temperature Stress-free temperature (SFT) is the below SFT, the rail contracts, creating tensile temperature at which there are no thermal thermal stress. The SFT is determined based stresses in the continuous welded rail (CWR). on several factors such as local climate, rail At SFT, the rail is laid and stressed so that at material properties, railway usage, and safety this temperature the rail is neither in tension considerations (Lim, Park, and Kang 2003). (due to cooling) nor in compression (due to The target neutral temperature is generally heating). For temperatures above SFT, rail 75 percent of the expected maximum tends to expand, leading to compressive temperature of the region (Savonis, Burkett, thermal stress. Conversely, for temperatures and Potter 2008). Another tactic is to adopt a seasonal stressing regimen, adjusting rail stress to suit winter and summer conditions (Dobney et al. 2009). Alternatively, infrastructure can be adapted, such as by replacing traditional ballasted tracks with continuous concrete slab tracks, which, although less maintenance-intensive and used in German high-speed lines, do generate more noise (Palin et al. 2013). Technology plays a crucial role, with IoT devices and sensors providing early warnings of extreme temperatures (Sanchis et al. 2020). Sensors, particularly optical fiber sensors, are used in various ways for railway monitoring. They detect temperature and strain changes, critical for assessing rail expansion and potential damage. They measure and provide precise location-specific data, enabling real-time monitoring (Ilie and Stancalie 2016). The development and implementation of these sensors are seen as having the greatest initial impact, particularly for rail defect monitoring (Chinowsky et al. 2019). Additionally, the application of certain coatings and paints on rails can help reduce the average temperature 30 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies gain, further protecting the infrastructure from temperature-induced stress (Network Rail Sensors, particularly 2025). Detailed information about various mitigation strategies for impacts on rail transport optical fiber sensors, are due to heat and increased temperature are discussed in table C.2. used in various ways for railway monitoring. They Recommendations and Next Steps detect temperature and strain changes, critical for Railways face multiple vulnerabilities during extreme heat events, from track deformation assessing rail expansion to equipment failure. The following recommendations outline key actions to enhance and potential damage. railway resilience, safety, and operational continuity during heatwaves while addressing They measure and provide current knowledge gaps. precise location-specific data, enabling real-time ● Support research. In the context of railway infrastructure resilience against monitoring. temperature-induced deformations such as sun kinks, there are noteworthy limitations in current research and practice that merit attention. A prominent gap is the absence of an established methodology to prevent sun kink deformations (Chinowsky et al. 2019). The rail industry relies on materials that strike a balance between global manufacturing standards, cost-effectiveness, and durability, which may not always be optimally resistant to such thermal stress (Chinowsky et al. 2019). This limitation underscores the need for innovative materials research to enhance rail robustness specifically against temperature fluctuations. ● Generate speed guidelines. Existing speed guidelines for trains during high temperatures suffer from a lack of specificity to local climatic conditions (Chinowsky et al. 2019). These guidelines are often based on broader regional or national standards and may not be sufficiently tailored to the microclimatic variables affecting specific track segments. Hence, there is a call for research into localized speed management protocols that can be dynamically adjusted to real-time environmental conditions. ● Address economic hurdles and knowledge gaps. From an infrastructural perspective, proposals for track design alterations to combat temperature-related issues face economic hurdles, particularly because of the high short- to medium-term costs (Chinowsky et al. 2019). These financial implications are a significant deterrent to rapid implementation, indicating a need for cost-benefit analyses that support the long-term economic viability of such design changes. ● Support data-driven decision-making. Any modification of existing speed regulations in response to thermal expansion risks must be grounded in strong empirical evidence (Chinowsky et al. 2019). This requirement denotes a requirement for rigorous, data- driven research to substantiate the need for and effectiveness of revised speed rules. Finally, the development of advanced sensor technology, which has been identified as having the most immediate impact on mitigating thermal damage to railways, requires more robust support. Investment in sensor technology research is critical, suggesting an opportunity for partnerships between industry stakeholders, technology developers, and academic institutions to accelerate innovation in this space (Ilie and Stancalie 2016). 31 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies Plane during take-off in the hot summer heat. AIR TRANSPORTATION—Key Findings Photo: 4kodiak. ● Rising temperatures significantly impact airport infrastructure such as runways and aircraft performance, requiring aircraft weight restrictions and longer takeoff distances. A recorded slab surface temperature of 56.4℃ at an airport when the ambient temperature was 34℃ highlighted the extent of thermal stress on airport pavements. ● As few as 10 percent of flights may currently face weight restrictions, but this could rise to 30 percent in the future, reducing payload and passenger capacity. ● Indirect impacts include compromised staff and passenger comfort, risk of equipment malfunction, altered tourism demand, and altered aircraft noise profiles. ● Mitigation strategies include proactive pavement and HVAC diagnostics, runway maintenance, and the construction of longer runways to accommodate reduced lift and engine power. ● Rescheduling flights to cooler times of day can moderately reduce the need for disruptive weight restrictions. Climate change is a pressing global issue with far-reaching consequences, and its impacts are particularly evident in the air transportation sector. Increased temperatures, a key component of climate change, are exerting significant pressure on air travel, posing challenges to the safety, reliability, and efficiency of aviation infrastructure and services. Heatwaves can affect aircraft performance and may cause airplanes to impose cargo restrictions, flight delays, and cancellations (see box 2.5). For example: In 2017, a heatwave in Phoenix, Arizona, led to dozens of American Airlines flight cancellations when 32 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies temperatures increased to 119°F—above the operable limit of several types of aircraft (Worland 2021). Extreme heat events, exacerbated by climate change, can also cause thermal expansion of runways and taxiways, leading to cracks and surface distortions. These surface defects can pose safety hazards to aircraft and disrupt airport operations. Rising temperatures can also affect the performance of aircraft engines, particularly those powered by jet fuel (US EPA 2016). In view of the significant adverse impacts of increased temperatures on air transport, it is imperative to adopt effective adaptation strategies. These strategies may include utilizing heat-resistant materials for runways and taxiways, implementing early warning systems for extreme weather events, and developing aircraft with improved heat tolerance and engine efficiency. By adopting proactive adaptation strategies, the resilience of the air transportation sector can be enhanced in the face of a changing climate, ensuring that air travel remains a safe, reliable, and efficient mode of transportation. This section considers the intricate relationship between rising temperatures and air transportation, examining the multifaceted impacts and exploring potential adaptation strategies. Weight Restrictions Caused by Heat Runway pavement at airports is particularly vulnerable to rising temperatures, with slab dilations occurring due to the high temperature differences between the top and bottom surfaces of the concrete slabs. This was exemplified by a recorded runway slab surface temperature of 56.4℃ when the ambient temperature was only 34℃ (Hodáková et al. 2019). This thermal stress affects the integrity of airport pavements and could lead to an increased need for maintenance and repair. The performance of aircraft is also directly affected by higher temperatures. As temperature rises, air density decreases, which in turn diminishes the lift generated by aircraft wings. This necessitates weight restrictions on aircraft, potentially decreasing their maximum takeoff weight (MTOW) and requiring longer takeoff and landing distances. An increase of 1°C has been correlated with a 100-foot increase in mean airport density altitude, impacting flight operations. On average, 10–30 percent of annual flights departing during daily maximum temperatures may face some level of weight restriction, with an expected mean restriction range of 0.5–4 percent of total aircraft payload and fuel capacity by the mid- to late-twenty-first century. For a Boeing 737-800, a 0.5 percent decrease from MTOW can equate to a reduction of three passengers or 2 percent of its passenger capacity (Coffel, Thompson, and Horton 2017). Larger aircraft—such as the Boeing 777-300 and the Boeing 787-8—will see greater impacts from these restrictions, potentially leading to a 3–5 percent reduction in total payload capacity and affecting 30–40 percent of flights by the 2080s. In contrast, mid-sized aircraft such as the Airbus A320 and Boeing 737-800 are less severely impacted, with only a 0.5 percent reduction in payload capacity and 5–10 percent of flights facing restrictions by the 2080s. These impacts also depend on specific airport characteristics, such as runway length and local temperature conditions. For instance, New York LaGuardia Airport and Dubai 33 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies BOX 2.5 High Summer Temperatures Impact Airport Capacity Worldwide Sky Harbor International airport, as temperatures reached 120°F (48.8°C)— that is, above the maximum operating temperature for many passenger planes. Solutions ● Schedule departures away from the hottest part of the day (more early morning and late evening departures) ● Similar practice followed in hot areas such as the Middle East. ● Aircraft manufacturers are offering a “hot and high” option on some of their Three aircrafts of TAP airline Heat-Induced Impacts aircraft to provide extra thrust and larger amidst the summer heat aerodynamic surfaces to make up for haze. Photo: Natallia Pershaj. ● In Greece, all 10 airports were the loss of lift, with no change to range characterized by high summer or passenger capacity. temperatures and short runways as of ● Lengthening runways is a structural 2017. A warming of 1.35°F (0.75°C) per solution, although this may not be decade has been observed since the possible at all airports. 1970s. ● The maximum takeoff weight has been Recommendations reduced by 280 pounds (127 kilograms) each year—equivalent to one less Policy makers should consider the trade-offs passenger every year. between aircraft traveler limits, scheduling ● In 2017, many flights were canceled restrictions, and longer runways to respond entirely over a few days at Phoenix’s to the extreme heat. Sources: Gratton et al. 2020 and Prisco 2023. International Airport experience significant weight restrictions on a large percentage of their flights, with expected payload capacity reductions of up to 3.5 percent and 6.5 percent respectively by the 2080s (Coffel, Thompson, and Horton 2017). There are indirect impacts to air travel as well. The comfort of staff and passengers within terminals may be compromised due to overloaded heating, ventilation, and air conditioning (HVAC) systems, and sensitive electronic equipment is at risk of malfunctioning. Climate events, such as sustained high temperatures, can cause substantial damage to airport infrastructure (Burbidge 2016). Furthermore, higher temperatures could alter the geography and seasonality of passenger and cargo demand, as seen in Greece where tourism volume is expected to decrease by 50 percent during peak summer months (Thomas, Jaarsma, and Tutert 2013). Aircraft noise profiles may also get louder because 34 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies of altered power settings and performance characteristics needed in warmer conditions. Moreover, the increased need for cooling equipment is expected to alter energy demands at airports; the Armstrong New Orleans Airport anticipates an increase in cooling needs offset by a decrease in heating requirements (Thompson 2016). Lastly, the potential fire hazard from aviation fuel exceeding its flash point on hot days and the connectivity of airports to mass transit systems are considerations that need to be factored into a holistic approach to mitigating the effects of temperature rise on air transportation networks (Thomas, Jaarsma, and Tutert 2013). Detailed impacts on air transport and corresponding magnitude of impacts are presented in table D.1. Heat Response: Extending Runways and Rescheduling Flights In response to the challenges posed by rising temperatures and heatwaves, airports are Airports are adopting adopting various mitigation strategies to preserve infrastructure integrity and ensure various mitigation operational efficiency. Regular diagnostics of airport pavements and HVAC systems have strategies to preserve become a norm, allowing for the early detection of potential issues caused by extreme infrastructure integrity heat. These diagnostics lead to proactive maintenance activities, ensuring that pavements and ensure operational can withstand the thermal stress and HVAC systems can cope with increased cooling efficiency. Regular demands during heatwaves. Furthermore, considering the impact of high temperatures on diagnostics of airport aircraft performance, there is a strategic move toward the construction of longer runways. pavements and HVAC Longer runways can accommodate the increased takeoff distances required by aircraft systems have become a under high temperature conditions when air density is lower, which affects lift and engine norm, allowing for the performance (Thomas, Jaarsma, and Tutert 2013). early detection of potential issues caused by extreme Another adaptive strategy is the rescheduling of flights. By moving flights with high heat. takeoff weights (TOWs) to cooler times of the day, airports can reduce the need for weight restrictions that would otherwise be necessary during hotter periods. This approach not only maintains safety but also minimizes disruption to both passenger travel and cargo transport schedules, which is crucial for maintaining the economic viability of airlines and airports alike (Coffel, Thompson, and Horton 2017). These strategies represent a concerted effort to maintain air transport reliability in the face of a changing climate, ensuring that the sector remains resilient to the increasing frequency and intensity of heat-related events. Detailed information about various mitigation strategies for impacts on air transport due to heat and increased temperature are discussed in table D.2. Recommendations and Next Steps Rising temperatures pose increasing challenges to air transport operations. Addressing these climate impacts requires coordinated action across multiple areas, though current efforts face policy gaps and funding limitations. Priority recommendations include: ● Encourage advancements in technology and strategic planning. Addressing the challenges posed by rising temperatures to air transport will require significant advancements in technology and strategic planning. Key areas of focus include enhancing engine performance and airframe efficiency, enabling aircraft to 35 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies operate more effectively under warmer conditions. Despite the potential benefits, implementing such technological changes presents several hurdles. ● Reschedule flights. One practical strategy under consideration is the rescheduling of flights—specifically those with high TOWs—to cooler hours, which may mitigate some temperature-related issues. However, the adoption of this strategy across the industry is hindered by several factors. One major limitation is that official positions and policies regarding adapting to a hotter climate are lacking in the aviation sector (Burbidge 2016). This gap leads to a lack of clear guidance and information, which in turn hampers the effective risk assessment necessary for developing robust response strategies. ● Secure additional funding. Financial constraints also play a critical role, as the resources required for research, development, and implementation of new technologies and procedures are substantial. Many stakeholders in the industry perceive it as early to allocate significant investments for climate change adaptation, particularly in regions where the impacts are not yet acutely felt. The combination of these challenges underscores the complexity of addressing the implications of temperature rise for air transport. It suggests a need for coordinated efforts among governments, industry players, and financial institutions to develop targeted research, clear guidance, and dedicated funding to prepare for and respond to the evolving climate reality (Burbidge 2016). Additionally, technological changes including improvements in engine performance and enhancement in airframe efficiency will be required (Coffel, Thompson, and Horton 2017). Kuwait, constructing longer runways is one adaptation tactic for areas expected to experience greater intensity and more frequent heatwaves. Photo: urbazon 36 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies A Transmilenio bus stop on a highway in Bogotá, Colombia PUBLIC TRANSPORTATION—Key Findings provides shade for waiting passengers. Photo: Arturo Rosenow. ● Rising temperatures lead to decreased public transportation ridership as people avoid heat discomfort, especially in low-income areas. ● Conventional bus stops, often made of heat-retaining materials, can become uncomfortably hot, sometimes reaching temperatures that pose a risk of skin burns (with metal bench seats averaging 39.7°C and spiking up to 50°C). ● In the United Kingdom, cooling panels and industrial fans at train stations have effectively reduced ambient temperatures. ● Malaysia’s experiments with different roofing materials have favored opaque concrete-based tiles for thermal comfort. Additionally, smart ventilation systems, such as those in Barcelona’s metro, optimize air quality and temperature while minimizing energy use. ● Mitigation strategies focus on redesigning bus stop geometry and materials and integrating renewable-powered cooling, assisted by technologies such as smart ventilation systems. ● Non-structural strategies also help; these include providing free water stations, disseminating heatwave alerts, and creating shaded areas and mist systems. In Paris, shaded areas augmented with water mist systems have been established to create comfortable microclimates. ● There are barriers to optimizing ventilation systems. These include the complexity of materials testing and validation processes, of integrating innovative climate solutions with existing infrastructure, and of addressing social inequalities in access to heat mitigation as well as the costs of additional cooling equipment. 37 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies Public transit infrastructure, such as bus stops and train stations, can also be significantly impacted by increased temperatures. Without adequate protective infrastructure that provides thermally comfortable conditions for public transit riders, it can be challenging to reach sustainability and public health goals in hot climates. Extreme heat events can also affect the performance of public transport vehicles. Buses and trains can experience overheating, reductions in efficiency, and increases in emissions under extreme heat conditions. Passenger comfort is another critical concern under rising temperatures. Public transport vehicles often lack adequate ventilation and air conditioning, making them uncomfortable and even hazardous during heatwaves. This can lead to reduced ridership, particularly among vulnerable groups such as the elderly and those with health conditions. Extreme Heat and Public Transit Ridership Rising temperatures have a tangible impact on public transportation systems, manifesting most noticeably in decreased ridership. Heat discomfort discourages the use of transit services, particularly where frequency is low, compounding the inconvenience of longer waits with the unpleasantness of high temperatures. This effect is exacerbated in low- income areas, where the drop in ridership is more pronounced, suggesting a correlation between economic status and the ability to avoid heat-exposed transit situations. The United Kingdom witnessed this phenomenon in July 2022, when record-breaking temperatures led to a marked decline in the number of passengers on the London Underground as people opted to work from home to escape the heat (Transport for London 2022). Similarly, in the United States, bus ridership showed a notable decrease of 0.3 percent on days where the mercury rose to or above 85°F, the 90th percentile temperature. The downward trend was steeper in lower-income neighborhoods, which saw a decrease of 1.6 percent compared to wealthier areas. Even medium-income communities saw a 1 percent drop, underscoring the pervasive impact of heat on public transit service use (Ngo 2019). The design and material choice for infrastructure such as bus stops can further contribute to decreased comfort and potential health risks for passengers. In instances of extreme heat, conventional bus stops—often made of materials that retain heat—become especially uncomfortable and potentially hazardous. Studies have shown that bus stop surfaces can reach temperatures that pose a risk of skin burns, with metal bench seats averaging 39.7°C and sometimes spiking up to 50°C (Dzyuban et al. 2022). Warming Sun Belt cities turn to cool pavement to help mitigate climate change. Metro systems in hot climates face three critical heat-induced vulnerabilities: (1) material Photo: ASCE fatigue, such as occurred in elevated lines where Bangkok’s BTS Skytrain experienced summer rail temperatures exceeding 60°C, leading to accelerated infrastructure deterioration (UNDRR 2025); (2) underground heat build-up, such as occurred in Chennai’s metro platforms, which reached 34°C–37°C, exceeding comfort limits; and (3) increased passenger health risks, such as occurred with Delhi Metro, which recorded a 20 percent spike in on-platform fainting incidents during the May 2024 heatwave (IPCC 2022). Passenger surveys reveal that every 1°C rise above 32°C increases “unsafe heat” perception by 6–8 percent among riders (IPCC 2022). 38 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies Informal transportation systems are disproportionately vulnerable to heatwaves because their vehicles are typically older, overcrowded, and lack air conditioning, with cabin temperatures reaching 39°C during extreme heat. This particularly impacts low-income passengers who become “captive” users forced to endure dangerous conditions or forgo essential trips (Ankhi and Khan 2025; Wright et al. 2025; Wright et al. 2024). Interestingly, the presence of trees and shelter at bus stops has mixed effects on mitigating these impacts. While shelters in Austin, Texas, did not significantly offset the effects of high temperatures on ridership, with shelters being placed at locations experiencing higher temperatures, a 1 percent increase in tree canopy in some areas correlated with a 1.6 percent lower decrease in ridership, indicating that natural shade can provide some relief (Lanza and Durand 2021). These findings point to the need for adaptive changes in public transportation infrastructure to improve comfort and maintain ridership levels in the face of rising temperatures. Public transport authorities need to re-evaluate material choices for infrastructure, focus on designing cooler transit facilities including bus stops, increase the frequency of services, and incorporate natural or artificial shading solutions to enhance passenger comfort during heat events. Detailed impacts on public transport and corresponding magnitude of impacts are discussed in table E.1. Hydration Initiatives In response to the challenges to public transportation posed by rising temperatures, various mitigation strategies have been developed to enhance comfort and safety. Bus stop designs are being reimagined, with considerations for geometry, materials, and the integration of renewable energy-powered cooling techniques (Montero-Gutiérrez et al. 2023). In the United Kingdom, for instance, innovative cooling panels and industrial fans have demonstrated the capacity to significantly reduce ambient temperatures at station (Transport for London 2022). Material testing and smart technologies are also being implemented. Malaysia’s experiment with different roofing materials has shown significant differences in thermal comfort, favoring opaque concrete-based tiles over translucent plastic roofs (Goshayeshi et al. 2013). Smart ventilation systems, such as the one tested in Barcelona’s metro network, utilize artificial intelligence (AI) to optimize air quality and temperature while minimizing energy use (TMB and SENER 2020). The adoption of radiative cooling panels in Kazakhstan—using materials that lower ambient temperatures via water circulation—has also shown promising results in reducing thermal indexes (Alikhanova et al. 2019). Shelters that incorporate sustainable design elements, such as radiant cooling systems with solar power production, show considerable promise in reducing surface temperatures and thermal load. Non-structural elements are also playing a key role in alleviating heat stress. The provision of free cold-water refill stations encourages hydration among passengers, while reminders to carry water are disseminated during heatwaves (Network Rail 2025). Beyond hydration, these strategies encompass creating a more comfortable microclimate by establishing 39 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies shaded areas, sometimes augmented with water mist systems, as seen in Paris (Montero- Gutiérrez et al. 2023). Furthermore, strategies include resilient task forces for forecasting, monitoring weather and infrastructure temperatures, and modifying travel advice during extreme heat conditions (Network Rail 2025). These are complemented by initiatives such as providing shaded areas and water sprinklers and strategically planting trees to provide natural cooling effects. Detailed information about various mitigation strategies for decreased public transportation trips due to heat and increased temperature are shown in tables E.2 (structural) and E.3 (non-structural). Recommendations and Next Steps To address the challenges posed by rising temperatures, public transport authorities can implement a range of mitigation strategies such as infrastructure upgrades, vehicle modifications, heatwave preparedness plans, and public awareness campaigns. However, Covered bus stop in Kuala Lumpur, Malaysia. this presents a series of practical and research limitations. Several recommendations for Photo: T. M. Yusof actions that can assist in resolving these issues follow. 40 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies ● Ensure that ventilation systems operate optimally. A key issue is ensuring the optimal operation of ventilation systems. While smart and dynamic control methods that adjust to both interior and exterior ambient conditions offer a potential solution, these require complex and precise optimization strategies to send individual setpoints to fans, depending on varying conditions through time and day (TMB and SENER 2020). The materials used in such systems must also balance energy efficiency and sustainability, posing a significant challenge in material selection and design. ● Validate climate parameters. The experimental processes required to validate the climate parameters impacting these design processes are intricate and time- consuming. This validation is crucial for understanding how proposed systems will function in real-world conditions, yet it remains a significant barrier because of the complex interactions of climate factors (Montero-Gutiérrez et al. 2023). ● Employ additional cooling equipment. The implementation of additional cooling equipment is often necessary to maintain thermal comfort, which introduces additional costs and considerations for energy consumption and infrastructure adaptation. Integrating innovative climate conditioning solutions, such as sustainable urban drainage systems (SUDs) or geothermal technology, with existing urban infrastructure is complex and has not been widely achieved, with many systems lacking cooling elements entirely or the innovative technologies that allow for self-sufficiency (Montero-Gutiérrez et al. 2023). ● Address social inequities. Social inequalities also play a role in the effectiveness of heat mitigation strategies. In the United States, for instance, wealthier neighborhoods Person waiting for the bus with higher incomes tend to have greater tree canopy cover, offering better natural under a bus shelter. Photo: YvanDube cooling, than poorer areas. This highlights a disparity in the lived experience of heat, suggesting the need for a more equitable approach to planning and implementing shade and cooling measures (Jones, Gwata, and Akoon 2022). ● Shift focus back to natural and passive cooling. Finally, there is a shift in focus from planning for shade—historically a significant aspect of urban design—to other forms of climate control, such as air conditioning, which has been made more accessible by cheaper electricity. This trend has contributed to a decreased prioritization of natural and passive cooling strategies like shading in urban planning. 41 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies Men riding cycle rickshaws in ACTIVE TRANSPORTATION—Key Findings Rajasthan, India. Photo: hadynyah ● There is a noticeable decline in active transportation usage across multiple cities, especially cycling, once temperatures exceed thresholds of 25°C–35°C, indicating an avoidance of active transit during extreme heat. ● Heat impacts active transportation comfort levels and health/safety: studies show slowed response times and heightened risk perceptions for cyclists at temperatures above 30.4°C. Infrastructure damage also challenges active transit. ● Urban design elements such as shading, greenery, and ventilation significantly influence active transit thermal comfort. Shade plans along cycleways are a crucial mitigation strategy. ● Mitigation strategies such as artificial wetting, advanced pavements, green roofs, and urban agriculture have quantifiably reduced heat indexes by 2.5°C–4.5°C, enhancing thermal comfort. ● Current seasonal projections probably overestimate future active transit usage rates by not fully accounting for the deterrent effect of higher temperatures. More adaptive research and policies are needed. Evaluating the effect of extreme heat and increasing temperatures due to climate change on active transportation modes, such as walking and cycling, is crucial for developing effective adaptation strategies that protect public health and maintain sustainable mobility options during extreme weather events. High temperatures and increased humidity make outdoor activities such as walking and cycling riskier, as the body struggles to cool itself effectively, leading to conditions such as heat stroke​​(Eltahir and Krol 2022). This risk is heightened for people engaged in active transportation, as they are directly exposed to 42 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies the outdoor environment. Rising temperatures can impede people’s ability to engage in outdoor activities, thus limiting active transportation options such as walking and biking​​ (Tait 2011). In an era where promoting active transportation is crucial for both health and environmental reasons, extreme heat can act as a deterrent, preventing people from choosing these healthier, more sustainable modes of transport. Urban areas suffer from the UHI effect, where temperatures can be significantly higher than those of surrounding areas​​(Eltahir and Krol 2022). The evaluation and The evaluation and mitigation of extreme heat’s impact on active transportation is critical mitigation of extreme for ensuring public health and safety, promoting sustainable transport options, and heat’s impact on active guiding urban planning and policy decisions in the face of climate change challenges. There transportation is critical is a considerable body of research showing the local cooling effects of heat mitigation for ensuring public health strategies. These strategies include increasing greenspace, using reflective and permeable and safety, promoting pavements, and implementing cool roofs—all of which improve outdoor thermal comfort sustainable transport by reducing neighborhood air temperature and environmental radiation. Implementing options, and guiding such strategies in areas with high heat vulnerability or high ambient temperature readings urban planning and policy can provide thermal comfort for pedestrians and active travelers. However, determining the decisions in the face of most effective use of these strategies, considering travel behavior, mode, and route choice, climate change challenges. remains a complex task. Prioritizing areas with heavy travel and combining environment and travel behavior changes can offer the best protection for active travelers. Heat and the Worldwide Decline in Cycling In the context of climate change and its effects on active transportation, several key impacts need to be considered. First, there is a noticeable change in demand and trip patterns, with evidence from various cities—such as Toronto and Montreal in Canada; Singapore; cities in the Netherlands; and Melbourne, Australia as well as Boulder, Colorado; Portland, Oregon; and Montpelier, Vermont in the United States—indicating a decline in active transportation usage, especially cycling, as temperatures exceed certain thresholds. For instance, temperatures above 28°C in Montreal led to a noticeable shift from cycling to sheltered transport modes; similar patterns were observed in other cities, highlighting a tendency to avoid active transportation during extreme heat conditions (Miranda-Moreno and Nosal 2011). Furthermore, comfort levels during active transportation are significantly affected by heat, impacting health and safety. Studies from Singapore (Meng et al. 2016) and San Francisco (Mislan, Wethey, and, Helmuth 2009) have shown that hot and humid conditions slow cyclists’ response times and elevate risk perceptions, particularly at temperatures above 30.4°C. Additionally, infrastructure wear due to high temperatures, such as pavement defects, further complicates active transportation. There is also a variation in how different purposes of trips respond to heat. In Singapore, cyclists commuting for work or school were more likely to switch to other modes, while those cycling for leisure would postpone their trips (Meng et al. 2016). This trend was similarly observed in the Netherlands, indicating leisure trips are more weather-sensitive than commuter trips (Helbich, Böcker, and Dijst 2014). 43 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies The impacts of heat on active transportation comfort levels have been further understood by incorporating parameters such as mean radiant temperature (MRT) and physiological equivalent temperature (PET), which consider factors such as air temperature, solar radiation, wind speed, and humidity. Optimal conditions for cycling, as noted in the Netherlands, included a maximum air temperature of 24°C, MRT of 52°C, and PET of 30°C, with cycling activities occurring mostly in cooler morning or evening times during hotter days (Böcker and Thorsson 2014). Australian studies further highlighted that urban design elements—such as street trees and tall buildings—significantly influence comfort levels in active transportation, with less shaded areas experiencing reduced comfort (Sun et al. 2021). Detailed impacts on active transportation and corresponding magnitude of impacts are presented in table F.1. Effect of Tree Canopies In addressing the impacts of extreme heat and temperature rise on public transit due to climate change, various mitigation strategies have been proposed and implemented globally. Shade plans play a crucial role in these strategies. For example, the Australian Institute of Environmental Health’s policy recommends creating shade along cycleways and outdoor dining areas using trees and other structures. Similarly, Abu Dhabi’s Public Realm Design Manual emphasizes “continuous shade” for a significant portion of walkways and public parks. Tel Aviv and Maricopa County in Arizona have also adopted guidelines for shading public streets and pedestrian routes (Turner, Middel, and Vanos 2023). The effectiveness of these strategies is underscored by the reduction in air temperatures they can achieve, with shading and greenery lowering temperatures by up to 4.5ºC (Chàfer et al. 2022). In Switzerland, for instance, different types of trees—such as silver lindens and field maples—have been shown to reduce the Universal Thermal Climate Index (UTCI) significantly, improving the thermal comfort of people during active travel (Kubilay et al. 2021). Tree-planting programs and increasing shade along travel routes are pivotal, as vegetation not only provides shade but also enhances thermal comfort through evapotranspiration. However, it is important to balance vegetation density and type to avoid obstructing ventilation. Bike path in Girona, Spain, Additionally, artificial wetting methods, such as the wetting of porous pavements, have under vine-covered railway been found to reduce UTCI by about 2.5°C. The implementation of advanced pavement viaduct. Photo: ioanna_alexa. technologies, green and white roofs, forced evaporative cooling, and urban agriculture further contribute to mitigating heat effects (Kubilay et al. 2021). Ensuring access to hydration, shade, and parks is also essential. For instance, a study in Singapore showed that a significant percentage of cyclists checked weather information before traveling, indicating the importance of informed decision-making in mitigating heat effects on active transportation (Meng et al. 2016). Detailed information about various mitigation strategies for decreased active transportation trips due to heat and increased temperature are discussed in table F.2. 44 Heatwaves and Transportation Infrastructure: Impacts, Consequences, and Mitigation Strategies Recommendations and Next Steps The limitations in current research and policies regarding the impact of extreme heat on active travel, particularly in the context of climate change, highlight several key areas of concern. ● Estimate future rates of active transportation. One significant limitation is the potential overestimation of future rates of walking, bicycling, and transit use due to increased temperatures. This suggests that current projections may not fully account for the deterrent effect of higher temperatures on active transportation modes (Karner, Hondula and Vanos 2015). ● Provide specific information for different transit users. Furthermore, the specific information needs of different transit users, particularly cyclists, are not adequately addressed. Cyclists tend to prioritize temperature information more than drivers, indicating a need for more tailored weather information services for different modes of transit (Meng et al. 2016). ● Integrate shade into urban planning. The integration of shade as a central element in urban planning and policy development is not widespread (Turner, Middel, and Vanos 2023). This gap underscores the need for more sustainable and cost-effective solutions to mitigate the effects of extreme heat on public transit users. ● Support nuanced research. Collectively, these limitations point toward the necessity for more nuanced and adaptive research and policy frameworks that consider the varied needs of transit users and effectively address the challenges posed by rising temperatures in urban environments. People walking on a busy footpath in Thailand. 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In India, 16 percent of travelers would cancel trips. ● Activity timing shifts to cooler periods. Workers in the United States reduced labor time by up to an hour at temperatures above 85°F; the Chinese move activities from hotter to cooler times. ● Adaptation involves both physical acclimatization and psychological adjustment. Expectations and neutral temperature tolerance vary by season. ● Mitigation requires multifaceted strategies: improved weather information, pedestrian infrastructure, vegetation, shade provisions, and multimodal connectivity. ● Research limitations exist in holistically capturing impacts across travel dimensions, integrating findings into transport planning, and accounting for seasonal perception variations. Weather conditions such as temperature, precipitation, wind speed, and humidity directly impact people’s travel behavior in terms of their chosen mode of transport, how far they are willing to travel, and the duration of outdoor activities. These changes in behavior— mode choice, distance traveled, and time spent on activities—influence the usage of and demands on the overall transportation system across metrics such as traffic volume, 52 Heatwaves and Their Effects on Transportation Systems: A Comprehensive Review bicycle volume, and public transit ridership. Transportation system usage then results in externalities such as emissions output, congestion levels, safety issues, and travel times. These externalities ultimately feed back into weather dimensions through mechanisms such as the greenhouse effect. Analyzing the interconnections and relationships within this loop provides valuable insights for transportation and urban planners when assessing public mobility needs relating to weather events such as extreme heat or severe storms. Considerations span health and safety issues, modal choices and shifts, activity participation and timing, strategic infrastructure adaptations, and environmental impacts. Evaluating the effect of extreme heat and increasing temperatures due to climate change on user travel behavior, such as mode choice, travel distance, activity time, and corresponding adaptation strategies, is crucial. Extreme heat poses major health risks, decreased comfort, and safety issues for travelers. Evaluating changes in travel behavior helps transportation planners better understand risks and prepare safety measures. Extreme heat often leads people to shift modes of transportation to cooler or more convenient options. For example, people may shift from walking or biking to taking a bus or car in hotter temperatures. Understanding these shifts helps improve multi-modal planning. Studies show heatwaves influence when and for how long people engage in outdoor activities or travel. Understanding changes in activity duration and timing due to heat allows for scheduling and system capacity improvements. Looking at adaptive A cyclist during a heatwave at strategies such as providing shade and hydration stations, public cooling centers, dealer the bank of river Gnages support systems, and improving ventilation and air conditioning in public transit allows in Prayagraj, India. Photo: anil_shakya19. planners to directly address issues caused by extreme heat events. Effect of Heat on Workforce and Transport User Behavior In the context of climate change and increasing temperatures, research indicates significant shifts in travel behavior dimensions and trip patterns. A study from the Netherlands found that nearly 80 percent of daily bicycle flow fluctuations are attributable to weather changes (Thomas, Jaarsma, and Tutert 2013). In India, 36 percent of metro users indicated a likelihood of changing their transport mode in response to temperature variations (Jain and Singh 2021). Similarly, in New York, maximum temperature thresholds of 28.1°C for bike riding and 25.8°C for average distance cycled were identified (Heaney et al. 2019). Chinese data revealed a decline in the preference for airplane and express bus travel with every 5°C temperature increase (Li et al. 2021). Furthermore, extreme temperatures have varied impacts on outdoor activities: both extreme cold and extreme heat substantially decrease participation in outdoor activities. Activity times also shift with temperature changes. For example, in Greece, outdoor presence stabilizes in the morning at lower temperatures during summer, decreasing post-midday (Nikolopoulou and Lykoudis 2007) (see also box 3.1). In the United States, workers exposed to temperatures above 85°F reduced labor time by up to an hour, especially toward the end of the day (Graff Zivin and Neidell 2014). And in China, intraday activity substitutions from hotter to cooler periods of the day are observed (Fan et al. 2023). Activity reductions are also noted. In Greece, the overall presence of people in open spaces 53 Heatwaves and Transport User Behavior: Impacts, Consequences, and Mitigation Strategies significantly drops with rising temperatures, and in India, 16 percent of metro users are likely to cancel their trips during high temperatures (Jain and Singh 2021). In China, hourly temperatures above 30°C and 35°C depress outdoor leisure activities by 5 percent and 13 percent, respectively (Fan et al. 2023). Finally, trip perception varies with temperature. In the Netherlands, temperatures above 25°C negatively affect en-route place valuations, while in Algeria, a positive outlook is observed among regular visitors familiar with an area when they visit during high temperatures (Boumaraf and Amireche 2020). In the United States, an inverted U-shaped relationship was observed for leisure activities, with a significant decrease in outdoor leisure at temperatures above 100°F (Graff Zivin and Neidell 2014). This nuanced effect on trips highlights the varied impacts of climate change on travel and outside leisure behavior, necessitating adaptive measures in transportation planning and policy. Detailed impacts of heat on user behavior and corresponding magnitude of impacts are discussed in table F.3. The health and safety of transportation systems staff is another important heatwave impact. In South Africa, for example, some 15 million people rely on minibus taxis as their primary mode of transport, with drivers spending 11 hours per day in these vehicles. A study by the South African Medical Research Council and the World Bank City Resilience Program found that temperatures reach 39°C within these vehicles, causing significant health issues for workers and passengers—particularly those with high susceptibility to heat related illnesses including elderly people, those with heart disease and diabetes, pregnant women, and infants (Wright et al. 2025; Wright et al. 2024). Long-haul truck drivers face substantial physiological risks during heatwaves, as prolonged Long-haul truck drivers exposure in vehicle cabins without adequate air conditioning can lead to dehydration, heat face substantial stress, fatigue, and impaired cognitive performance (Apostolopoulos, Lemke, and Sönmez physiological risks during 2014; Birdsey et al. 2015; NIOSH 2016). Studies document that high cabin temperatures heatwaves, as prolonged increase driver fatigue and slow reaction times, elevating the risk of accidents and driving exposure in vehicle cabins errors (Dabaghi, Dehghan, and Shakerian 2023; Wu et al. 2023). Laboratory and field without adequate air research confirms that even moderate heat (for example, 27°C cabin temperature) reduces conditioning can lead to driver vigilance, with a 22 percent increase in reaction time and 50 percent more missed dehydration, heat stress, alert signals than in cooler conditions (Wu et al. 2023; Wyon, Wyon, and Norin 1996). fatigue, and impaired Vehicle cabin conditions such as lack of functional cooling, insufficient rest areas, and the cognitive performance. inability to access shaded parking further exacerbate these vulnerabilities (Lise et al. 2024). Mechanically, heatwaves heighten the risk of tire blowouts, engines overheating, and degradation of vehicle electronic components, directly threatening safety and operational reliability (Bechtold 2024). These evidence-based first-order impacts make it critical to implement heat mitigation and cabin cooling measures to protect driver safety and maintain road transport integrity during extreme heat events. Heatwaves increase the physiological risks faced by construction and maintenance workers on transport infrastructure projects. Prolonged exposure to extreme heat can cause heat stress, dehydration, heat exhaustion, and, in severe cases, life-threatening heat stroke—especially during physically demanding outdoor activities (WHO 2024). The risk is 54 Heatwaves and Transport User Behavior: Impacts, Consequences, and Mitigation Strategies Hot Weather by BOX 3.1 compounded the strenuous Impacts nature on Public Spaceof construction Usage work, which heightens internal body in Arid Algeria Impacts on the Use of Public Space ● People tend to stay in public spaces for less time during the summer than the winter. ● Microclimatic conditions are less desirable in the summer; these conditions include strong sunshine and wind. ● Areas offering shade and water features are popular even during the summer. ● Those individuals who were most sensitive to climatic parameters were people over 60 years old. ● “Visual construct” (how people perceive the atmosphere of a space) depended A sidewalk by a large avenue in Oran, Algeria, with huge trees that provide shade for pedestrians. Photo: Bruno Malfondet. primarily on the perception of a pleasant atmosphere by the people. Mitigation Steps ● People who frequented the site regularly and knew the space well felt the high ● Vegetation, shade, and the presence of temperature was an asset (Boumaraf a water feature are elements that make and Amireche 2020). people stop at a place. temperature and accelerates fluid loss, impairing both physical and cognitive performance (Echt et al. 2020). Studies show that a large proportion of heat-related occupational deaths occur among workers performing moderate to heavy labor, often within the initial days of exposure or without adequate acclimatization (ILO 2019). Effect of Shaded Walkways and Vegetation Islands Adaptations to travel behavior in response to extreme heat and increased temperatures involve both physical acclimation and psychological adaptation. Studies from China (Fan et al. 2023) and Qatar (Alattar and Indraganti 2023) published in 2023 indicate that behavioral adaptations, such as avoiding the hottest parts of the day, are more developed than physical acclimation. In Qatar, people living in naturally ventilated traditional houses showed an ability to adjust to a wide range of thermal conditions. Psychological adaptations are also evident. In Qatar, the neutral temperature tolerance differs between warm and cool seasons (Alattar and Indraganti 2023), and in South India (Deevi and Chundeli 2020), the neutral temperature range is higher than the standard. Additionally, people’s expectations vary with the season, affecting their thermal comfort levels. These data underscore the importance of considering both physical and psychological factors in adapting travel behavior to climate change. 55 Heatwaves and Transport User Behavior: Impacts, Consequences, and Mitigation Strategies Mitigating the impacts of extreme heat and increased temperatures on travel behavior requires a multifaceted approach. First, improved weather information provision and infrastructure preparedness are crucial for protecting pedestrians and cyclists and reducing accident rates in adverse weather conditions (Meng et al. 2016). Green route environments, with their aesthetic appeal, also play a vital role. Routes with multiple urban locations and buildings are perceived as less aesthetically appealing, while compact urban morphologies adjacent to these routes can alleviate undesirable weather exposures. Pedestrian-friendly infrastructure that is adaptable to all weather conditions, coupled with better multimodal connectivity and dynamic information systems, is essential. Evidence-based recommendations from WHO, the US Occupational Safety and Health Administration (OSHA), and the US National Institute for Occupational Safety and Health (NIOSH) include providing cool, accessible drinking water (at least 1 cup every 15–20 minutes); frequent rest breaks in shaded or air-conditioned areas; job rotation; and modifying work schedules to cooler parts of the day (OSHA 2023). Employers should also offer training on heat-related illness prevention, monitor environmental heat conditions, and ensure that workers—especially new and unacclimatized ones—receive longer and more frequent breaks to reduce the risk of adverse health outcomes (NIOSH 2024). Furthermore, features such as vegetation, shade, and the presence of water significantly enhance the attractiveness of public spaces, encouraging people to stop and use these areas. Strategies such as providing shaded walkways and waiting areas, utilizing high Shaded footpath in height-to-width ratios for effective shading, and creating vegetation islands that act as Ahmedabad, Gujarat, India for people to walk to and shelter corridors are effective (Dzyuban et al. 2022). These measures not only improve from home, work, recreational aesthetic appeal but also offer practical solutions to reduce heat exposure for travelers. facilities, schools, shops, and public transportation. Photo: Detailed information about various adaptation strategies for changes in user behaviors are Fahad Puthawala discussed in table F.3 Recommendations and Next Steps Research on travel behavior under extreme heat and rising temperatures due to climate change faces several limitations. Recommended actions fall into four main categories: ● Incorporate multiple dimensions in studies. Predominantly, studies often focus on single dimensions of travel behavior, whereas a more holistic approach incorporating multiple dimensions—such as activity time and participation along with mode choice and trip distance—would yield more comprehensive insights. ● Integrate impacts and meteorological observations into planning. There is a gap between these impacts and existing transport planning processes. Many studies do not distinguish between the effects of short-term weather and long-term climate, which is a crucial factor considering how the perception of temperatures varies with seasons. Furthermore, thermal comfort measures in these studies have not effectively replaced 56 Heatwaves and Transport User Behavior: Impacts, Consequences, and Mitigation Strategies observed meteorological variables, and most analyses are limited to daily trip patterns without considering intra-day substitutions (Liu, Susilo, and Karlström 2017). ● Utilize cost-benefit analyses. Crucially, the impact of weather on social benefits and cost estimates in cost-benefit analyses is often overlooked. This oversight extends to large-scale transport models that typically do not account for weather variations. The changing relationship between traffic speed, flow, and density under different weather conditions is another underexplored area. ● Enhance policy and planning considerations. Finally, policy and planning considerations— such as the inclusion of shade as a heat-mitigation strategy—are not adequately addressed in current studies, with evidence suggesting only minimal focus on such strategies in urban planning. The adaptation of autonomous vehicles to adverse weather conditions also remains an area needing more attention (Liu et al. 2017). References Alattar, D. and M. Indraganti. 2023. “Investigation of Outdoor Thermal Comfort and Psychological Adaptation in Hot-Humid Climate of Qatar.” E3S Web of Conferences 396: 05015. https://www.e3s- conferences.org/articles/e3sconf/abs/2023/33/e3sconf_iaqvec2023_05015/e3sconf_iaqvec2023_05015.html Apostolopoulos, Y., M. Lemke, and S. Sönmez. 2014. “Risks Endemic to Long-Haul Trucking in North America: Strategies to Protect and Promote Driver Well-Being.” New Solututions 24 (1): 57–81. https:// doi.org/10.2190/NS.24.1.c. 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Tutert. 2013. “Exploring Temporal Fluctuations of Daily Cycling Demand on Dutch Cycle Paths: The Influence of Weather on Cycling.” Transportation 40: 1–22. https://doi. org/10.1007/s11116-012-9398-5 WHO (World Health Organization). 2024. Climate Change, Heat and Health. Fact Sheet, May 28, 2024. World Health Organization. https://www.who.int/news-room/fact-sheets/detail/climate-change-heat- and-health Wright C. Y., T. Kapwata, S. Kunene, N. Kwatala, N. Mahlangeni, T. Laban, and C. Webster. 2025. “Heat in the Transport Sector: Measured Heat Exposure and Interventions to Address Heat-Related Health Impacts in the Minibus Taxi Industry in South Africa.” International Journal of Biometeorology (2025). https://doi.org/10.1007/s00484-025-02935-2 Wright, C. Y., T. Kapwata, N. Mahlangeni, N. Naidoo, and C. Webster. 2024. “Assessing Heat-Related Health Perceptions in the Minibus Taxi Industry in Tshwane, South Africa.” South African Journal of Science 120 (11/12). https://doi.org/10.17159/sajs.2024/18030 Wu, Z., T. Jin C. Chen, X. Li and J. Yan. 2023. “How Do Different Ambient Temperatures and Vehicle Speeds Affect the Cognitive Performance of Male Drivers? Evidence from ERP.” Traffic Injury Prevention 24 (3): 271–78. https://doi.org/10.1080/15389588.2023.2181078 Wyon, D. P., I. Wyon, and F. Norin. 1996. “Effects of Moderate Heat Stress on Driver Vigilance in a Moving Vehicle.” Ergonomics 39 (1): 61–75. https://doi.org/10.1080/00140139608964434 58 Heatwaves and Transport User Behavior: Impacts, Consequences, and Mitigation Strategies 4 Additional Considerations Delhi Metro train arriving at Jhandewalan metro station in Key Findings New Delhi, India Photo: rahul sapra. ● The benefit of reducing critical vulnerability should be assessed. Direct costs, externalities (unintended spillover effects such as increased public health burdens, reduced worker productivity due to delayed commutes, or broader economic slowdowns caused by disruptions in freight transport)—and social costs in the transportation sector should be better quantified and included in the investment prioritization. ● Regional climates and differences in infrastructure age must be included in the assessment and preparation for the impacts of heat on road networks. ● Optimizing investments requires assessing critical vulnerabilities and prioritizing mitigation and adaptation measures. ● Climate impacts on transportation are unequally distributed: In Delhi, women are 20 percent more likely than men to cancel metro trips due to heat, while 45 percent of women change their access mode compared to 27 percent of men. ● Income creates significant disparities: In San Francisco, heat exposure for travelers is 65 percent higher for the lowest income quintile than it is for the highest, and 4.9 times greater for zero-vehicle households than for those with four or more vehicles. ● Age affects vulnerability: Studies in Algeria found that people over 60 face disproportionate sensitivity to high temperatures, so they alter their travel behaviors. ● Infrastructure interdependencies create cascading vulnerabilities when heat affects power systems and information and communication technology (ICT) networks that support transportation. ● Technological innovations such as thermochromic materials and phase change material-impregnated pavements offer significant temperature regulation benefits for transportation infrastructure. Still, low-tech solutions remain vital. Simple measures such as shade structures, protective clothing, and public awareness campaigns complement complex technological interventions. ● Systemwide adaptation is essential because each infrastructure component has unique failure thresholds under extreme heat conditions. 59 Their Effects Heatwaves and Transport UseronBehavior: Transportation Impacts, Systems: A Comprehensive Consequences, Review and Mitigation Strategies Fresh mist shower at a bus Prioritizing Investment stop on a hot summer day in Kyoto, Japan. Photo: TokioMarineLife. Optimizing investment requires assessing critical vulnerabilities and prioritizing mitigation and adaptation measures. Investment prioritization is important in different mitigation and adaptation options for transportation infrastructures. Several classifications of mitigation and adaptation strategies exist, including short-term mitigation and long-term adaptations, reactive and proactive strategies, and data-driven and opinion-based strategies. The costs and benefits of each strategy vary over time. The benefit of reducing critical vulnerability should be assessed, among other points. In general, direct costs, externalities, and social costs in the transportation sector should be better quantified and included in the investment prioritization. Excessive heat affects the productivity of workers (García-León et al. 2021), increases hospital admissions, and leads to heat-related morbidity and mortality (Vicedo-Cabrera et al. 2021); this ultimately undermines people’s health as well as economic growth (Burke, Hsiang, and Miguel 2015). For example, it has been recently estimated that the heat mortality cost of urban heat islands in European cities is, on average, €192 per person per year (Huang et al. 2023), and the latest estimate of the social cost of carbon emissions is $185 per metric ton of carbon dioxide (CO2) (Rennert et al. 2022). Such information should be combined with risk assessment and cost-benefit analysis tools specifically tailored to the transportation sector in order to inform planning and prioritize future investments. 60 Heatwaves and Transport User Behavior: Impacts, Consequences, and Mitigation Strategies Regional Differences Regional assessments from the Unlivable series, particularly the Europe and Central Asia volume, reveal clear geographic disparities in urban heat exposure and infrastructure vulnerability (World Bank 2025). The Europe and Central Asia report projects that cities such as Bucharest, Istanbul, and Athens may experience more than 10,000 cumulative heat- related deaths by 2050 under moderate emissions scenarios, emphasizing the urgency of spatially differentiated strategies (World Bank 2025). Integrating insights from these regional studies can enhance the calibration of heat adaptation strategies in transport by aligning them with context-specific vulnerabilities and expected exposure levels. Regional climates must Regional climates must be part of the assessment and preparation for the impacts of be part of the assessment heat on road networks. Various pavement standards exist across the world; each of these and preparation for depend on local construction standards and climatic conditions, with certain types of roads the impacts of heat on and materials that are more or less vulnerable to heat. road networks. Various pavement standards exist Regional differences are not the sole determinant of the impact of heatwaves on across the world; each transportation infrastructure, however. For instance, the age of the infrastructure is also of these depend on local important. Older infrastructure in milder climates may be more vulnerable than newer construction standards and infrastructure in areas with extreme climates. climatic conditions, with certain types of roads and Investment prioritization differs across regions. Regions with limited water resources may materials that are more or need to prioritize water usage for purposes other than cooling pavements, while those with less vulnerable to heat. plentiful water can afford to use that water to address the direct impacts of heatwaves. Likewise, heatwave impacts vary across regions, as illustrated by a UK report regarding the effects of climate change on railroads (Ferranti et al. 2016). While urban areas face intensified impacts due to the urban heat island effect and higher infrastructure use, disruptions propagate through entire transportation networks. Failures in cities can lead to downstream effects in rural and peri-urban regions due to the interconnectedness of national and regional mobility systems. Rural and intercity connectivity—including freight corridors and access to essential services—is equally critical for resilience planning. Countries can benefit from the experiences of regions that have dealt with heat-related infrastructure challenges. For example, the experiences of the United Arab Emirates in managing heat’s impact on infrastructure could provide valuable lessons for other countries facing similar issues. However, solutions must be tailored to local conditions. Solutions such as using water or trees for cooling may not be universally applicable because their effectiveness depends on local climate, water availability, and drought conditions. Assessing the vulnerability of transport infrastructure should be based on the population it serves. This assessment should focus on high-population areas, especially urban ones, where the impact of transport vulnerability is maximized. The age of the infrastructure and the income level of the country in which it is located are major variables in assessing vulnerability (Bobb et al. 2014). Developed countries face unique challenges, including latency and lifespan reduction in infrastructure due to various conditions (such as extreme heat events damaging 61 Heatwaves and Transport User Behavior: Impacts, Consequences, and Mitigation Strategies electrical grids and freeze-thaw cycles deteriorating road surfaces), highlighting the need for location-specific tailored solutions (Bobb et al. 2014; Coffel, Thompson and Horton 2017; Greenham et al. 2020). On the other hand, developing countries confront an urgent need for heat-resilient transport systems (Chinowsky et al. 2011). Planners should also consider the likelihood of transport failure and the severity of its consequences, particularly in high-population areas. Conditions that have changed since the infrastructure was originally engineered and local relative temperature changes could pose significant challenges to infrastructure. The number of days exceeding certain temperature thresholds is a critical factor for infrastructure, especially for rail transport, where high temperatures can cause issues such as rail buckling. Developing transferable methods to assess the impacts and adaptation across regions will enable more consistent and effective climate resilience planning for transportation infrastructure worldwide (Mittal and Ukkusuri 2025; Mittal, Ukkusuri and Arroyo Arroyo 2022; Schulz, Zia, and Koliba 2017; Wang et al. 2020). Climate Inequality Climate change, characterized by increased temperatures and extreme heat, presents significant challenges for transportation infrastructure and services. However, the impacts of these changes are not uniformly distributed across populations. A critical dimension of these impacts is equity— the fair distribution of both the burdens (such as upfront costs) and the benefits (such as more sustainable transportation systems) arising from mitigating The impacts of climate change (Klinsky and Dowlatabadi 2009; Mittal et al. 2023). The impacts of extreme extreme heat and heat and high temperatures on transportation infrastructure and services raise important high temperatures equity concerns. Equity assessment is crucial to understanding how different demographic on transportation groups are affected and to developing targeted strategies to mitigate these inequities. infrastructure and Marginalized groups—including lower-income individuals, racial and ethnic minorities, services raise important women, children, the elderly, and those with disabilities—often face disproportionate risks equity concerns. Equity from climate change (Eltahir and Krol 2022). assessment is crucial to understanding how Specific evidence substantiates the disproportionate impacts of heat on transportation different demographic access and safety across social factors such as income, gender, race, age, and disability groups are affected and status: to developing targeted strategies to mitigate these Income inequities. ● In Oregon in the western United States, bus ridership on very hot days decreased 1.6 percent in lower-income neighborhoods compared to only 1 percent in middle-income and no change in high-income tracts (Ngo 2019). ● In San Francisco, the United States, heat exposure for travelers was 65 percent higher for the lowest income quintile than for the highest, and 4.9 times greater for zero- vehicle households than for households with four or more vehicles (Karner, Hondula, and Vanos 2015). 62 Heatwaves and Transport User Behavior: Impacts, Consequences, and Mitigation Strategies ● In Austin, the United States, the CapMetro determines whether a bus stop qualifies for a shelter based on (1) daily boarding counts and (2) closeness to high-activity areas. This creates a systematic inequality between the rich and poor neighborhoods for availability of shelters for bus stops (Lanza and Durand 2021). ● In Australia, greater population density is correlated with less shade and a lower density of trees (Sun et al. 2021). Gender ● In Delhi, India, women were significantly more likely than men to cancel or adjust metro trips because of heat. Twenty percent of women who normally use the metro cancel their metro trips, compared to 10 percent of men; 45 percent of women change the access mode of metro, compared to 27 percent of men (Jain and Singh 2021). Women waiting for public transportation in Delhi. Photo: Pradeep Gaur ● In Australia, female cyclists were more deterred by unfavorable weather conditions than male cyclists (Ahmed et al. 2012). ● Heatwave days in the continental United States show a positive association with fatal traffic crashes involving both male (3 percent) and female (5 percent) drivers (Wu, Zaitchik, and Gohlke et al. 2018). ● Globally, males face a significantly higher road injury burden due to high temperatures compared to females, with males having an age-standardized mortality rate (ASMR) 63 Heatwaves and Transport User Behavior: Impacts, Consequences, and Mitigation Strategies of 0.54 and a disability-adjusted life year (DALY) rate of 27.31 per 100,000, whereas females have an ASMR of 0.18 and a DALY rate of 8.99 per 100,000 (He et al. 2023). Race ● In Salt Lake City, the United States, bus stop shelters were more prevalent in higher- income and less racially diverse areas (Miao, Welch, and Sriraj 2019). Age ● In Algeria, one study found that people over age 60 and 65 face a disproportionate sensitivity to high temperatures, altering their travel activities (Boumaraf and Amireche 2020). ● In Greece, individuals greater than 65 years of age show greater sensitivity to summer heat (Nikolopoulou and Lykoudis 2007). ● In New York, the United States, older cyclists took fewer bike rides (not shorter ones) on high-temperature days (Heaney et al. 2019). ● Health risks posed by extreme heat are particularly dangerous for young children, the elderly, and individuals with medical conditions such as heart disease (Eltahir and Krol 2022). ● The highest mortality rates are observed in males aged 25–49—especially in high Human Development Index areas, where rates have increased from 1990 to 2019— while rates for males of other age groups remained stable (He et al. 2023). ● In the Republic of Korea, young casualties consistently rise with influencing factors, including age-related cognitive ability, reaction speed, driving expertise, experience in Elderly ladies outside a church hazardous conditions, and tendencies for aggressive or risky driving (Park, Choi, and in the central square of the Chae 2021). village in Chios island, Greece. Photo: portokalis. Disability status ● Generally, disabled individuals face greater harm from heat events given their reliance on precarious transit services, higher rates of social isolation and outdoor exposure, and limited adaptive capacity (Alfonseca 2021). ● Lower-income groups, racial minorities, and disabled individuals disproportionately rely on active transportation to meet basic needs. There are equity concerns for marginalized groups relying on active modes (Gronlund 2014). The health risks of heat exposure are also unequal. Children, the elderly, those with medical conditions, outdoor workers, and lower-income groups tend to suffer greater harm at high 64 Heatwaves and Transport User Behavior: Impacts, Consequences, and Mitigation Strategies temperatures (CDC 2022). Where transit service is less reliable or nonexistent, individuals must endure dangerous conditions when traveling out of necessity. These inequities multiply pre-existing disadvantages. Mitigating the disproportionate impacts of heatwaves on transportation infrastructure and services requires a multi-faceted approach, including: ● Plan equitable infrastructure. Ensure that infrastructure, such as bus shelters, is evenly distributed, prioritizing areas with vulnerable populations. Incorporate shade and cooling features in urban design, especially in densely populated, low-income areas. ● Adjust planning criteria. Adjust planning criteria for public transit to serve vulnerable neighborhoods. Expand transit service during extreme temperature events to provide accessible cooling centers and mitigate disrupted mobility for marginalized groups. ● Upgrade infrastructure for marginalized areas. Develop walking/cycling infrastructure upgrades focused on low-income areas and socially vulnerable groups. Prioritize shade and universal accessibility. ● Target policies and programs. Develop and implement policies that specifically address the needs of the most affected groups, such as the elderly, children, low- income populations, and those with medical conditions. ● Enhance awareness and preparedness. Increase awareness and create public outreach campaigns about the risks of extreme heat; provide guidelines for safe travel during heatwaves, especially targeting vulnerable groups. Provide multilingual guidance on risks, protective actions, and accessing support. ● Foster community engagement: Engage with local communities to understand their specific needs and challenges and incorporate their input into planning and decision- making processes. Climate change multiplies environmental harms for disadvantaged populations. Transport agencies and decision-makers must correct historic inequities in adapting infrastructure for extreme heat. Centering social equity principles in research and policy can help redirect adaptation investments to the highest-need areas while building just and resilient transportation systems. Interdependent Systems A key aspect of understanding the impacts of rising temperatures and extreme heat is understanding the interdependence of infrastructure systems, which means that heat risks to energy and ICT networks can significantly affect transport resilience. The interdependence of infrastructure is increasingly apparent in the face of climate change. 65 Heatwaves and Transport User Behavior: Impacts, Consequences, and Mitigation Strategies For instance, the functionality of power systems directly affects railways, where electrified routes can sag and contract under extreme heat. Additionally, heatwaves negatively impact road infrastructure, influencing supply chains, accessibility, safety, and the reliability of transportation infrastructure (Luisa 2019). Heatwaves can trigger cascading disruptions across interconnected transport systems. For instance, a failure in rail service due to track buckling may overload road networks and increase heat-related risks there. These effects are magnified in dense urban areas, where modal substitution and shared infrastructure— such as power grids or cooling systems—can create compounding vulnerabilities. Increasingly frequent, Increasingly frequent, intense, and prolonged heatwaves and extreme weather events pose intense, and prolonged risks to transportation infrastructure, workforce, and travelers. Addressing these challenges heatwaves and extreme requires a multifaceted approach: there is no one-size-fits-all solution to infrastructure and weather events pose resilience issues. It is also particularly challenging for low- and middle-income countries that risks to transportation need substantial investment in new transportation infrastructure and maintenance to achieve infrastructure, workforce, the United Nations’ Sustainable Development Goal 9, which is to “build resilient infrastructure, and travelers. Addressing promote inclusive and sustainable industrialization and foster innovation” (UN DESA, no these challenges requires date). In developing nations, this situation is exacerbated by already-existing vulnerabilities in a multifaceted approach: infrastructure, which often lack the agility or design to adapt to changing climatic conditions. there is no one-size-fits-all solution to infrastructure The concept of decoupling highlights the gap between current infrastructure design and and resilience issues. evolving climate conditions. This issue is particularly worrisome for older infrastructures in both developed and developing countries, which are less capable of adapting to changing conditions. The interdependence of infrastructure requires considering both the system’s weakest links and its keystones—the critical components with numerous connections. Understanding these interconnections is essential to identifying and fortifying critical points within the transportation network to enhance overall resilience. Vulnerabilities propagate across entire transport networks—urban, rural, and intercity— highlighting the need to understand differences in infrastructure agility and design requirements in diverse contexts. Ensuring continuity of services, especially along critical trade and access corridors, is essential for resilience and equitable development. Cities are often critical nodes within wider transport networks, and disruptions at these points can cascade through national and international corridors (Jaroszweski et al. 2015). However, resilience planning must also prioritize rural connectivity and intercity links to maintain supply chains and regional mobility, particularly in low-density areas that depend on fewer transport options. To mitigate the impacts of climate change on transportation infrastructure and services, it is vital to understand the interdependencies of different infrastructure systems, develop adaptable and resilient infrastructure, and ensure equitable distribution of resources and efforts to protect all communities. This approach involves not only technological and structural adaptations but also considers socioeconomic factors and prioritizes vulnerable populations. Integrating resilience into everyday practices and planning processes, as well as ensuring flexibility in funding and infrastructure development, are key steps toward building a more resilient and equitable transportation system in the face of climate change. 66 Heatwaves and Transport User Behavior: Impacts, Consequences, and Mitigation Strategies Technological Innovations With rising temperatures and extreme heat, technological advancements are vital for adapting transportation infrastructures. These advancements have introduced materials such as thermochromic substances, which regulate temperature in varying conditions. Despite their high cost and their susceptibility to photodegradation under ultraviolet (UV) solar radiation, these materials offer significant temperature-regulating benefits. Another important advancement is the development of heat storage enhancement techniques, such as phase change material (PCM)-impregnated pavements, graphite powder–filled pavements, and heat-harvesting pavements with renewable energy components. These technologies aim to effectively regulate surface temperatures, offering a more resilient infrastructure against extreme heat. Moreover, advanced manufacturing techniques, including the use of polymer-modified binders, are becoming essential in adapting transportation infrastructures to a wider range of temperatures. However, these modifications often come at an increased cost. Internet of Things (IoT) devices and sensors also play an indispensable role, particularly in railway systems, where they provide early warnings of extreme temperatures and help prevent rail defects. The application of specialized coatings and paints on rails further protects the infrastructure from temperature-induced stress. The economic implications of track design alterations and other infrastructural changes to combat temperature- Bus stop with cooling panels in Bangkok, Thailand. Photo: related issues are significant. These financial constraints can deter rapid implementation, pigphoto. 67 Heatwaves and Transport User Behavior: Impacts, Consequences, and Mitigation Strategies highlighting the need for cost-benefit analyses that support the long-term economic viability of such design changes. The design of transportation infrastructure is also undergoing changes to combat temperature-related issues. For example, in the United Kingdom, stations are being reimagined with innovative cooling panels and industrial fans, demonstrating significant reductions in ambient temperatures (TfL 2022). The adoption of radiative cooling panels, as seen in Kazakhstan (Alikhanova et al. 2019), has shown promising results in reducing thermal indexes, with materials that lower ambient temperatures through water circulation. And shelters incorporating sustainable design elements, such as radiant cooling systems powered by solar energy, are proving effective in reducing surface temperatures and thermal load. Transportation infrastructure departments are also moving away from designs based on historical climate records and are instead considering how temperatures may change over the infrastructure’s lifespan. This shift is driven by the need to counteract the increasing stress on infrastructure, utilities, and manufacturing as heatwaves push materials and equipment beyond their current temperature thresholds. These technological advancements and design alterations are part of a broader strategy to adapt to the challenges posed by climate change. There is an increasing shift toward infrastructure designs that consider projected temperature changes over their lifespan rather than relying solely on historical climate data. This shift is essential, given the record-breaking heatwaves seen in recent years and the expected worsening of such events in many parts of the world, particularly in Africa, Central and South America, and Southeast Asia. Simple, low-tech solutions are also important. These include uncomplicated solutions such as using umbrellas and hats for personal heat protection, and they include quick, inexpensive actions that all cities can support. Along these lines, timely information; behavioral changes; and practical, everyday solutions to coping with increased heat—alongside more complex technological and infrastructural adaptations—are significant. In the same low-tech way, a signal about heatwaves can be seen in stores that prominently displaying various sunscreens, subtly communicating the importance of personal sun protection; this is an innovative approach to public health communication. Protective measures such as wearing sunglasses are vital for safeguarding children’s eyes against harmful UV rays. References Ahmed, F., G. Rose, M. Figliozzi, and C. Jakob. 2012. “Commuter Cyclist’s Sensitivity to Changes in Weather: Insight from Two Cities with Different Climatic Conditions.” Paper prepared for theTransportation Research Board Annual Meeting, Washington, DC, January 2012. Transportation Research Board. https://www.researchgate.net/publication/311220138_Commuter_Cyclist’s_Sensitivity_ to_Changes_in_Weather_Insight_from_Two_Cities_with_Different_Climatic_Conditions Alikhanova, A., A. Kakimzhan, A. Mukhanov, and L. 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Gohlke. 2018. “Heat Waves and Fatal Traffic Crashes in the Continental United States.” Accident Analysis & Prevention 119: 195–201. https://doi.org/10.1016/j. aap.2018.07.025 70 Heatwaves and Transport User Behavior: Impacts, Consequences, and Mitigation Strategies 5 Overarching Recommendations and Next Steps A digital thermometer at Key Findings a bus stop displays a high temperature of 39°c during a summer heat wave in Madrid, ● A heatwave action roadmap with recommended action plans could help to Spain. Photo: Jose Gonzalez Buenaposada. understand and adapt to heatwave impacts on transport. ● Proactive actions, which are much less costly than reactive actions, can mitigate the impacts of heatwaves in a cost-efficient manner. ● Regional collaboration and regular evaluation based on public health indicators will be central to developing adaptive plans. ● Working across sectors and scales while addressing combined risk factors is key to building resilience. ● Developing and implementing metrics to assess progress toward heat mitigation is crucial. ● Communication campaigns paired with early warning systems, worker safety policies during heatwaves, and accessible indoor cooling facilities form indispensable risk management. ● Coordinating initiatives across different sectors and jurisdictions is essential. ● Updated regulations, policies, and codes addressing heat risks require development while exchanging insights globally. The integration of resilience into infrastructure design and planning, coupled with strategic policy efforts and collaboration across sectors, is key to building transportation systems that are not only technologically advanced but also equitable and sustainable in the face of a changing climate. 71 Their Effects Heatwaves and Transport UseronBehavior: Transportation Impacts, Systems: A Comprehensive Consequences, Review and Mitigation Strategies Future Principles and Next Steps of Heat Resilience As the impacts of climate change intensify and become increasingly evident, developing resilience principles and plans to mitigate urban heat is crucial—especially in developing nations, which often lack the resources to adequately respond (Ukkusuri et al. 2024). This section proposes future principles and next steps for heat resilience, focusing on strategies pertinent to developing nations. Develop a Heat Action Roadmap With the conducted review and gathered information, a heatwave action roadmap should be constructed. This should incorporate recommended action plans for mitigating and adapting to heatwave impacts on transportation infrastructure and users. The roadmap would be used by transport agencies, practitioners, think tanks, and development agencies that are starting their effort to understand and adapt to heatwave impacts on transport. Transportation stakeholders seeking to address extreme heat impacts should consider developing their own context-specific heat action roadmap. While each city and region faces unique challenges and opportunities, several potential phases and elements could inform this process: ● Baseline assessment considerations. Transportation agencies might begin by characterizing heat vulnerabilities through stakeholder identification, meteorological projections, infrastructure impact assessments, resilience evaluations, and climate monitoring methods. The specific approaches should be tailored to local contexts and existing institutional frameworks. ● Feasibility and toolkit development possibilities. Agencies may find value in resource allocation assessments, action planning, investment prioritization, cost- benefit analyses, and identifying relevant mitigation strategies. The methodologies and focus areas would necessarily vary based on regional priorities, existing infrastructure conditions, and available resources. Future work could also inform the development tools to support transportation agencies, including climate-screening platforms, asset- level heat-risk checklists, and readiness matrices that help to assess vulnerability and readiness at the project level and systematically integrate climate considerations into design typologies and maintenance protocols. ● Long-term adaptation planning options. Cities might explore adaptability mechanisms, regional collaboration approaches, resilience standards development, and community engagement strategies that reflect their unique social, economic, and environmental contexts. 72 Heatwaves and Transport User Behavior: Impacts, Consequences, and Mitigation Strategies Address Heat Vulnerabilities in Marginalized Communities ● Advance equity in adaptation planning. Extreme heat disproportionately impacts marginalized communities, converging with other risk factors such as income inequality, inadequate housing, and lack of access to health care. Equity must be central in developing heat resilience plans. Studies show stark disparities in access to cooling and shade by income. For example, in Pakistan’s urban areas, only 5 percent of low-income residents are projected to have indoor cooling access by 2050, compared to 38 percent of high-income residents (Davis et al. 2021). Medellín, Colombia, targeted tree planting and “green corridors” in low-income neighborhoods (Nature 2021). Equity considerations should evaluate how proposed strategies, such as increased air conditioning access, might improve conditions for some while worsening emissions. Tree planting and shaded escalator in a low-income neighborhood in Medellín, Colombia. Photo: ● Scalable interventions for resource-constrained low- and middle-income countries. Deep shade structures at bus stops and stations have proven highly effective, with field trials in Phoenix showing reductions in physiologically equivalent temperature (PET) of up to 19°C for waiting passengers using inexpensive materials (galvanized sheet, polycarbonate, local timber) (Dzyuban et al. 2022). Similarly, cost-effective interventions include vegetated or reflective “cool” roofs on transport buildings that reduce surface temperatures by 15°C –20°C (World Bank 2025), tree- based linear green infrastructure along corridors that lower ambient temperatures by 1°C–3°C at street level (Marando et al. 2022), and cool or permeable pavements that 73 Heatwaves and Transport User Behavior: Impacts, Consequences, and Mitigation Strategies cut surface temperatures by 7°C–12°C with low incremental cost over standard asphalt (World Bank 2025). These interventions, supported by community-based heat action plans such as using telecommunications networks for early warning systems (Hasan et al. 2021), offer transport agencies and municipalities a pragmatic strategy that can be rapidly deployed and scaled across different contexts while delivering measurable improvements in infrastructure resilience and passenger comfort.strategy that can be rapidly deployed and scaled across different contexts while delivering measurable improvements in infrastructure resilience and passenger comfort. Establish Comprehensive Monitoring and Evaluation Systems ● Develop and implement metrics. Developing and implementing metrics to assess progress toward heat mitigation is vital. These metrics should be consistent and cover a range of scales and sectors spanning health outcomes, environmental data, and progress indicators. For example, public health officials may focus on heat-related illness prevention, while urban planners may concentrate on reducing neighborhood temperatures (Keith et al. 2021). ● Develop consistent metrics across domains. Conflating heat measures such as land surface (for example, Los Angeles reduced surface temperature by 4°C–6°C by using cool pavements) and mean radiant temperatures can misrepresent mitigation impacts (Middel et al. 2020). Expanded on-site monitoring globally is imperative as little empirical evidence on heat exposures exists for developing country or global south cities (Vicedo-Cabrera et al. 2021). ● Improve measurement and evaluation techniques. Enhanced evaluation approaches tracking post-implementation outcomes over both the near- and long-term present a vital need and opportunity. Emphasizing on-the-ground air temperature data, spatial heat distribution maps, regular progress monitoring, and centering shade amenities in development plans comprises a robust foundation for evidence- driven policies that eliminate inequities in heat vulnerability (Jones, Gwata, and Akoon 2022). Advanced computational modeling can also simulate the effects of various heat mitigation strategies on future temperature distributions, enabling ex-ante assessment of options suited to local geoclimatic contexts before large scale implementation. Tracking suite-of-solution impacts over both the near- and long-term post-deployment remains vital for iterative enhancement. Integrating data analytics, simulation methods, and monitoring comprises a robust foundation for equitable and scientifically informed heat resilience planning. Tracking the progress of mitigation strategies and developing methods to evaluate their impacts over time is crucial. Planning and policy should increasingly focus on shade, a currently underutilized aspect of heat mitigation (Keith et al. 2021). Deploy Evidence-Based Heat Mitigation and Risk Management Solutions ● Mitigate heat and weigh regional trade-offs. Land use regulations can mandate built environment mitigation strategies tailored to local contexts. These regulations can 74 Heatwaves and Transport User Behavior: Impacts, Consequences, and Mitigation Strategies Bus station with green roof in promote ventilation and reflect heat, mitigating the urban heat island effect. Vegetated Taiwan. Photo: Lim Weixiang - Zeitgeist Photos. green roofs, for example, reduce temperatures by 1.2 ̊C more than reflective cool roofs in drier California cities, while cool roofs show 0.2 ̊C additional cooling in humid Miami (Keith et al. 2021). Planners must weigh regional trade-offs between heat mitigation strategies and the defined goals. For example, in Los Angeles, cool pavements dramatically lower land surface temperature by 4°C–6°C but increase mean radiant temperature for pedestrians by 4°C (Middel et al. 2020). Trade-offs demand evidence- based decision-making with granular meteorological data, which enables response calibrated to local climates. ● Principles of priority actions. Integrated climate risk frameworks that quantify transportation asset vulnerabilities across hazards—including flooding, cyclones, and heat—help in prioritizing actions. Approaches such as damage estimation models and vulnerability-criticality assessments can be used. Integrate hazard interaction models that combine heat and flood risks, including the quantification of damage and vulnerability for critical assets. This supports prioritizing infrastructure investments where both exposure and systemic importance are high. ● Highlight costs of inaction. Emphasize the avoided costs of inaction, including deferred operations and maintenance, resilience dividends, and reductions in damage costs. For example, increasing pavement albedo via reflective coatings has been shown to reduce surface temperatures by up to 9 Kelvin and yield measurable energy or maintenance savings (Cheela et al. 2021). Although reflective pavement treatments have been shown to reduce surface temperatures by 2.5°C–6°C, proactive pavement design upgrades may cost approximately $60,000 per kilometer—significantly less than reactive repair costs projected later this century (Knott et al. 2019). 75 Heatwaves and Transport User Behavior: Impacts, Consequences, and Mitigation Strategies ● Avoiding maladaptation, multi-hazard trade-offs. Several heat adaptation measures create vulnerabilities to other climate hazards. Reflective pavements, while reducing surface temperatures during heatwaves, can increase condensation, snow, and ice buildup in colder conditions, creating slip hazards and heating penalties in winter (Yang, Wang, and Kaloush 2013). Polymer-modified asphalt designed for heat resistance shows significant strength degradation under repeated freeze-thaw events and wet-dry cycles (Kim and Le 2023). Heat-resistant rail infrastructure, including continuous welded rail systems, can increase the risk of track fractures during cold periods when rails contract, requiring careful calibration of neutral rail temperatures to avoid safety compromises (Association of American Railroads 2023). Additionally, green infrastructure and vegetated corridors, excellent for heat mitigation, present maintenance challenges and potential slip hazards during snow and ice conditions (Taguchi et al. 2020), while behavioral adaptations such as schedule changes to avoid midday heat may reduce service accessibility during cold snaps when demand for heated public transport typically increases (Batur et al. 2024). This evidence underscores the critical need for integrated, multi-hazard planning approaches that avoid creating new vulnerabilities while addressing heat resilience. ● Manage heat risks strategies. Communication campaigns paired with early warning systems, worker safety policies during heatwaves, and accessible indoor cooling facilities form crucial elements of risk management. Ahmedabad’s 2013 heat action plan exemplifies this approach through warnings and multilingual announcements, along with annual evaluation to enhance responsiveness over time. Regular assessment ensures equitable strategy reach. However, research on appropriate temperature metrics is lacking in developing nations. Public health outcomes should be tracked over time to continually improve response measures. Additionally, continual evaluation of such systems’ responsiveness and reach ensures protections apply equitably across neighborhoods and employment sectors (Keith et al. 2021). Foster Cross-Jurisdictional Coordination and International Collaboration ● Coordinate initiatives across jurisdictions. The effect of heat transcends jurisdictions. Coordinating initiatives across different sectors, businesses, and jurisdictions is essential (Challinor et al. 2018; Mittal et al. 2024). Inter-agency and cross-jurisdictional coordination provide integrated governance for the multifaceted challenge of heat. Dedicated heat resilience roles across planning, health, emergency response, housing, and other agencies facilitate unified efforts. Additionally, coordination at a regional scale enables amplification of strategies’ impacts since heat transcends municipal boundaries. Western Sydney’s 2018 extreme heat management plan demonstrates such extensive collaboration, where unified governance facilitates amplified regional impacts spanning 13 municipalities and multiple sectors (WSROC 2018). ● Build heat institutions and international collaboration. Updated regulations, policies, and codes addressing heat risks require development while exchanging 76 Heatwaves and Transport User Behavior: Impacts, Consequences, and Mitigation Strategies insights globally. Integrating “Cool Community Standards” into building guidelines and planning processes institutes resilience at multiple scales. Such policy frameworks remain scarce worldwide but offer immense promise, as evidenced by flood risk governance. Borrowing best practices from other areas such as flood governance can also be useful. International collaboration, such as through the Global Heat Health Information Network, is vital for sharing insights and building capacity (Keith et al. 2021). Building on the global shift toward life-cycle-based resilience planning, this report emphasizes integrated pillars of system planning and financing, engineering and design, operations and maintenance, contingency planning, and institutional capacity and coordination (Keou, Dehghani, and Breteau 2025). Conclusions By centering equity, coordinating governance, generating granular risk data, and mitigating hazards in context-specific ways, cities can chart heat resilient futures despite Regional collaboration limited resources. Regional collaboration and regular evaluation based on public health and regular evaluation indicators will be central to developing adaptive plans. Working across sectors and scales based on public health while addressing combined risk factors is key in building just resilience. Heat resilience indicators will be central to principles demand scaled application across urban governance to protect developing cities. developing adaptive plans. Underserved groups stand to gain most from comprehensive strategies. Working across sectors and scales while addressing These considerations represent potential starting points rather than prescriptive combined risk factors requirements. The specific processes, priorities, and implementation approaches should is key in building just be developed at the city level, informed by local climate projections, infrastructure resilience. Heat resilience vulnerabilities, institutional capacities, and community needs. Transportation agencies principles demand scaled should engage broadly with stakeholders and conduct regular assessments to develop and application across urban refine strategies that respond to their particular circumstances as climate conditions evolve. governance to protect developing cities. 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Stiller. 2020. “Solar Reflective Pavements—A Policy Panacea to Heat Mitigation?” Environmental Research Letters 15 (6): 064016. http://dx.doi. org/10.1088/1748-9326/ab87d4 Mittal, S., T. Yabe, I. Kumar, and S. V. Ukkusuri. 2024. “Spatial and Cross-Sectoral Relationships in Business Entry Dynamics around a Highway Corridor.” Transportmetrica A: Transport Science 20 (1): 2138627. https://doi.org/10.1080/23249935.2022.2138627 Nature. 2021. “Cities Must Protect People from Extreme Heat.” Editorial, July 14, 2021. https://www. nature.com/articles/d41586-021-01903-1 Taguchi, V. J., P. T. Weiss, J. S. Gulliver, M. R. Klein, R. M. Hozalski, L. A. Baker, J. C. Finlay, B. L. Keeler, and J. L. Nieber. 2020. “It Is Not Easy Being Green: Recognizing Unintended Consequences of Green Stormwater Infrastructure.” Water 12 (2): 522. https://doi.org/10.3390/w12020522 Ukkusuri, S. V., S. U. Park, S. Mittal, L. Chapman, G. Manoli, A. Santos, N. K. W. Jones, P. Ayner, and N. Romero. 2024. “We Need to Prepare our Transport Systems for Heatwaves—Here’s How.” Nature 632 (8024): 253–56. https://doi.org/10.1038/d41586-024-02538-8 Vicedo-Cabrera, A. M., N. Scovronick, F. Sera, D. Royé, R. Schneider, A. Tobias, . . . and A. Gasparrini. 2021. “The Burden of Heat-Related Mortality Attributable to Recent Human-Induced Climate Change.” Nature Climate Change 11 (6): 492–500. https://doi.org/10.1038/s41558-021-01058-x WSROC (Western Sydney Regional Organisation of Councils). 2018. Turn Down the Heat Strategy and Action Plan. Blacktown, NSW: WSROC. https://heathealth.info/wp-content/uploads/Western-Sydney- Turn-Down-the-Heat-Strategy-and-Action-Plan-2018-1.pdf World Bank. 2025. Guidelines on Integrating Nature‑Based Passive Cooling Options into Urban Planning and Design. Washington, DC: World Bank. http://documents.worldbank.org/curated/ en/099218102092342530 Yang, J., Z. Wang, and K. E. Kaloush. 2013. Unintended Consequences: A Research Synthesis Examining the Use of Reflective Pavements to Mitigate the Urban Heat Island Effect, Revised April 2014. Arizona State University National Center of Excellence for SMART Innovations. https://d3dqsm2futmewz.cloudfront. net/docs/smart/unintended-consequences-1013.pdf 78 Heatwaves and Transport User Behavior: Impacts, Consequences, and Mitigation Strategies Additional Readings Arasu, S. 2023. “India’s Warm Weather Plans Can’t Take the Heat, Report Says.” The Seattle Times, March 28, 2023. https://www.seattletimes.com/nation-world/indias-warm-weather-plans-cant-take-the-heat- report-says/ Kramon, C.. 2023. “As Heat Waves Increase, Los Angeles Is Coating Some Streets with ‘Cool Pavement’.“ Los Angeles Times, September 8, 2023. https://www.latimes.com/california/story/2023-09-08/heat- waves-los-angeles-reflective-coating-streets-cool-pavement Climate-ADAPT. 2020. Heat Health Action Plans. https://climate-adapt.eea.europa.eu/en/metadata/ adaptation-options/heat-health-action-plans C40 Cities Climate Leadership Group. 2021. Cool Surfaces: Experiences from C40’s Cool Cities Network. https://www.c40knowledgehub.org/s/article/Cool-surfaces-Experiences-from-C40s-Cool-Cities- Network?language=en_US Global Heat Health Information Network (GHHIN). 2025. Global Heat Health Information Network: Heat Health Risks. https://ghhin.org/ . Shi Hui, P. 2023. “Cool Solutions for a Hotter Climate: Tackling Urban Heat Island Effect with Innovation.” Sustainable Cities (blog), September 7, 2023. https://blogs.worldbank.org/sustainablecities/ cool-solutions-hotter-climate-tackling-urban-heat-island-effect-innovation Nordgren, J., M. Stults, and S. Meerow. 2016. “Supporting Local Climate Change Adaptation: Where We Are and Where We Need To Go.” Environmental Science & Policy 66: 344–52. https://doi.org/10.1016/j. envsci.2016.05.006 Rivera, J., P A. Arias, A. A. Sörensson, M. Zachariah, C. Barnes, S. Philip, S. Kew, R. Vautard, G. Koren, I. Pinto, M. Vahlberg, R. Singh, E. Raju, S. Li, W. Yang, G. A. Vecchi, L. J. Harrington, and F. E. L. Otto. 2022. Climate Change Made Record Breaking Early Season Heat in Argentina and Paraguay about 60 Times More Likely. World Weather Attribution. https://www.worldweatherattribution.org/wp-content/uploads/WWA-Argentina-Scientific-report.pdf Visram, T. 2022. “Meet the 7 Chief Heat Officers Who Are Making Their Cities More Resilient.” Fast Company, October 7, 2022. https://www.fastcompany.com/90793483/meet-the-7-chief-heat-officers-who-are- making-their-cities-more-resilient 79 Heatwaves and Their Effects on Transportation Systems: A Comprehensive Review Appendix A Road Pavements: Impacts and Mitigation Strategies Table A.1  Impacts on Pavements and Corresponding Magnitude of Impacts as Identified by Multiple Studies in the Area Impact Country (paper) Method Prediction year Magnitude of impacts Rutting United States$$$ System Dynamics + 1.8°C rise by 2100 Rutting is the primary cause of pavement failure. (Mallick et al. 2014) Mechanistic-Empirical Pavement Design Guide (MEPDG) United States$$$ AASHTOWare a 2060 • AC rutting increases by 9–45%. (Gudipudi, Underwood, Pavement ME • Total rutting increases by 5–34%. and Zaighout 2017) • Increases by 2.33% with 1% temperature rise. • More vulnerable at the top of pavement phenomena. United States$$$ MEPDG — • AC rutting increases by 0.036–0.134 inches (4–16%). (Meagher et al., 2012) • Greater for US interstates than secondary roads. United States$$$ AASHTOWare Pavement ME 2100 • AC permanent deformation increases by 0.1–0.31 (Stoner et al. 2019) inches for interstate (0.08–0.24 inches for primary road); life reduced up to 5 years for interstate roads (up to 8 years for primary roads). • Pavement life is reduced up to 8 years due to total permanent deformation for interstate (up to 6 years for primary roads). United States$$$ Review — Increased rutting (Daniel et al. 2014) Alligator United States$$$ System Dynamics + 1.8°C rise by 2100 Less than 10% cracking / (Mallick et al. 2014) MEPDG fatigue cracking United States$$$ AASHTOWare Pavement ME 2060 Higher by 2–11% (1.38% with 1°C increase) (Gudipudi, Underwood, and Zaighout 2017) United States$$$ MEPDG — • On secondary roads: Becomes less severe. (Meagher et al., 2012) • On interstates: Increases in coastal locations and decreases in inland locations United States$$$ AASHTOWare Pavement ME 2100 • Top-down fatigue cracking increases by 86 to 923 (Stoner et al. 2019) feet/mile for interstate roads • Pavement life is reduced up to 7 years United States$$$ Review — Thermal fatigue cracking increases with more freeze (Daniel et al. 2014) thaw cycles Joint faulting Global Review — Thermal expansion occurs at bridge joints (de Abreu, Santos, and Monteiro 2022) United States$$$ AASHTOWare Pavement ME 2060 Joint faulting increases for rigid pavements with higher (Gudipudi, Underwood, relative slab movement and Zaighout 2017) Longitudinal United States$$$ System Dynamics + 2100 Decreases with higher temperatures cracking (Mallick et al. 2014) MEPDG United States$$$ AASHTOWare Pavement ME 2060 Reduces as low shrinkage observed with rise in (Gudipudi, Underwood, temperatures and Zaighout 2017) Modulus of United States$$$ System Dynamics + 1.8°C rise by 2100 Reduces by 12.7% subgrade soil (Mallick et al. 2014) MEPDG 80 Heatwaves and Their Effects on Transportation Systems: A Comprehensive Review Impact Country (paper) Method Prediction year Magnitude of impacts Asphalt layer Global Review — Reduced asphalt-layer stiffness and strength stiffness / (de Abreu, Santos, and modulus of Monteiro 2022) HMA / resilient modulus United States$$$ MnPAVE b 2°C–4.5°C rise by Resilient modulus decreases by 14% (Knott et al. 2019) 2050 United States$$$ System Dynamics + 1.8°C rise by 2100 • Modulus of HMA reduces by 36% (Mallick et al. 2014) MEPDG • Maintenance cost of HMA overlay increases by 160% compared to 60% (without climate change) United States$$$ Review — Decreased stiffness (Daniel et al. 2014) International United States$$$ AASHTOWare Pavement ME 2100 • Changes by –0.74 inches to 14.02 inches / mile for Roughness (Stoner et al. 2019) interstate roads (–2.7” to 11.7”/mile for primary Index (IRI) roads) • Modest decrease in time to failure Australia$$$ Thornthwaite Moisture Index — Increases by 3 x more for annual maintenance without (Taylor and Philp 2015) (TMI) prediction systematic reconstruction Pavement life United States$$$ MnPAVE 2050 Spring and summer seasons contribute 90%+ of total and overall (Knott et al. 2019) 2°C–4.5°C rise pavement damage. damage United States$$$ System dynamics + 2100 Life decreases from 16 to 4 years (Mallick et al. 2014) MEPDG 1.8°C rise by 2100 Australia$$$ Lab experiments 4°C rise Number of traffic cycles to failure reduces by about 6 (Kumlai, Jitsangiam, and million Pichayapan 2017) Life decreases from 20 to 16 years Australia$$$ Thornthwaite Moisture Index — • Life decreases 2 × more for annual maintenance (Taylor and Philp 2015) (TMI) prediction without systematic reconstruction • Highest decrease for agricultural land but lowest for coastal land Economic Losses Global Infrastructure Planning 2050 Developing countries: (Bolivia$, Cameroon$$, Support System (IPSS) • Proactive adapt: Relatively low annual costs (Bolivia: Croatia$$$, Ethiopia$, $8.4 million, Cameroon: $5.7 million, Ethiopia: $6.6 Italy$$$, Japan$$$, New million) and high opportunity costs (Bolivia: 96%, Zealand$$$, Sweden$$$, Cameroon: 31%, Ethiopia: 40%) Philippines$$, Venezuela, • Reactive adapt: significant cost increase (Bolivia: $56 RB$$) million, Cameroon: $15 million, Ethiopia: $50 million); (Schweikert et al. 2014) opportunity cost increase (Bolivia: 165%, Cameroon: 51%, Ethiopia: 117%) Developed countries: • Proactive adaptation: high annual costs (Italy: $154 million, Japan: $436 million, Sweden: $104 million) • Reactive adaptation: significant cost increase (Italy: $534 million, Japan: $1.1 billion, Sweden: $121 million) Europe and United Superpave Performance 4°C rise • €3.3 billion increase in annual O&M road costs (€591/ Kingdom$$$ Grade system kilometer) (Mulholland & Feyen, • € 0.8 billion annual cost-mitigating emissions to 1.5°C 2021) • High rise in O&M costs for Eastern Europe: Romania (24%), Poland (33%), and Bulgaria (45%) Mexico$$ Infrastructure Planning 2050 • Cumulative fiscal cost: $1.3 billion–$4.8 billion (Espinet et al. 2016) Support System (IPSS) • Opportunity cost: 6–22% Source: Original table for this publication. Note: AC = asphalt concrete; HMA = hot mix asphalt; IPSS = Infrastructure Planning Support System; MEPDG = Mechanistic-Empirical Pavement Design Guide; O&M = operations and maintenance; TMI = Thornthwaite Moisture Index; — = not available; $$$ = high-income countries; $$ = middle-income countries; $ = low-income countries. a. AASHTOWare is a software suite developed by the American Association of State Highway and Transportation Officials (AASHTO). b. MnPAVE refers to Minnesota’s Pavement Design Software. It is a mechanistic-empirical pavement design program developed by the Minnesota Department of Transportation (MnDOT). 81 Appendix A. Road Pavements: Impacts and Mitigation Strategies Table A.2  Structural Mitigation Strategies for Pavements Strategy Country (paper) Details / Strategy effectiveness HMA thickness United States$$$ Increase HMA thickness or build base layer (Knott et al. 2019) Specifications (2.8°C rise): • Base layer is sound: Increase HMA thickness by 32% ($60,000 / kilometer) • Base layer fails: Rebuild base layer ($35,000 / kilometer) and replace HMA ($350,000 / kilometer) Material selection United States$$$ Overdesign of pavement structure considering climate forecasts most effective against (Gudipudi, Underwood, fatigue cracking and Zaighout 2017) Europe and United • Selection of pavement PG based on future temperatures Kingdom$$$ • Use alternative aggregate structure, modifier, or pavement structure within the same PG (Mulholland and Feyen minimizes road rut 2021) United States$$$ Planners should not consider temperature to be a stationary range but should plan to (Daniel et al. 2014) accommodate a range of climate variations to occur in the lifetime Australia$$$ • Asphaltic materials with harder binders (significant but costly) (Dawson 2014) • For a high range of temperature, changing binder is not best (it exhibits reduced ductility in cold). Binder property manipulation by polymer modifiers works best (significant but costly) Italy$$$ • Selection of temperature-susceptible materials such as asphalt binder by considering (Viola and Celauro 2015) whole service life • For PG 64–28, modification of polymer is necessary (but is approximately twice the cost) Material adaptation: Reflective Global Properties of reflective pavements: pavements (Qin 2015) • Areas exposed to great solar radiation • Decrease the pavement distresses, increase the durability • Low costs Asphalt (base albedo ~ 0.05–0.25): • Light-colored aggregate (albedo: 0.52): Temperature decrease by 4°C • Chip seal (albedo: 0.08–0.2): Temperature decrease by 10 °C, 5-6 °C per 0.1 albedo • High near-infrared paint (albedo: 0.09–0.66): Temperature decrease by 3.8°C–20°C (> 10°C mostly) Concrete (base albedo ~ 0.25–0.75) • White concrete (albedo: 0.37–0.8): Decreases with weathering; wetting increases Albedo • Additive slag (Albedo: 0.36–0.69): Albedo increases with slag • Whitetopping (Albedo: 0.34–-0.4) • Gray-cement pavement (Albedo: 0.35–0.4) Issues • Decrease temperature in winters also • More thermal stress for pedestrians • Effects decrease with aging Material adaptation: Thermo- Global Changes color based on temperature chromic materials (Qin 2015) • Concrete (base albedo ~ 0.40–0.80): High reflectance with TiO2 fusion (decreased strength) • Asphalt: 6°C cooler • Cement: 4°C–6°C cooler Issues: • High cost • Decreased strength (UV / visual optical filtering useful) 82 Appendix A. Road Pavements: Impacts and Mitigation Strategies Strategy Country (paper) Details / Strategy effectiveness Material adaptation: Evaporative Global • Evapotranspiration: Holds water for evaporative cooling pavements (Qin 2015) • Reduces the tire road interaction Porous Pavers (vegetated, reinforced turf, or grass paving) • Types: Plastic geocells with grass; open-celled paving grids with grass • Reduces temperature by 2.6°C for asphalt pavement and 1.6°C for concrete • Issue: Grass may die during long spells of heat Permeable Pavers (non-vegetated) • Types: Concrete bricks, concrete pavement stones, and pavers with infiltration cells • Cooler than asphalt pavement during day and warmer at night • Issue: More rehabilitation / maintenance (clogging dirt in cavity) Pervious Pavers Types: Pervious concrete, pervious asphalt concrete, concrete paste or asphalt binders coat large, single-grade aggregates Cools faster than normal concrete, especially after rain Issue: Aggravates UHI during drying spell Material adaptation: Water Global • Replenish water-retention: Sprinkling water automatically reduces temperature by retentive pavements (Qin 2015) 5°C–15°C (Shio Site, Tokyo) • Filler materials: { Blast furnace slab filler: Reduces temperature up to 10°C; cooling lasts 1 week; pavement life increases by 3 years { Water retentive fillers: Porous lower-H O/Al O geopolymer, porous ceramics 2 2 3 • Enhancing cooling: Thin water layer, arched water retention block Material adaptation: Heat Global PCM-impregnated pavements added to concrete suppresses 3°C–8°C, decreases strength storage enhancement (Qin 2015) Issues • No high traffic or heavy-vehicle loadings • High construction and maintenance Maintenance Global Proactive adaptation measures significantly reduce impacts and costs compared with reactive (Schweikert et al. 2014) scenarios Europe and United Frequent low-cost operations minimize maintenance costs Kingdom$$$ (Mulholland and Feyen 2021) Portugal$$$ Conducts crack seals after 3, 6, and 12 years of road construction; experiences significantly (Mulholland and Feyen lower relative costs 2021) Australia$$$ A = Repair as needed; B = Systematic annual maintenance; C = B + additional conditions. (Taylor and Philp 2015) Resealing/ reconstruction at 16 and 32 years • IRI values with regimen A and B are almost 3 × that for regimen C. • Pavement life 2 × lower for regimen A and B compared to regimen C. Source: Original table for this publication. Note: Both planning and material-based adoption are common. H2O/Al2O3 = Water/Aluminum oxide ratio geopolymer; HMA = hot mix asphalt; IRI = International Roughness Index; PCM = phase-change materials; PG = performance grade; TiO2 = titanium dioxide; UHI = urban heat island; $$$ = high-income countries; $$ = middle-income countries; $ = low-income countries 83 Appendix A. Road Pavements: Impacts and Mitigation Strategies Table A.3  Non-Structural Mitigation Strategies for Pavements Strategy Country (paper) Details Forums Latin America$$ Develop forums for deliberating goals (McAndrews, Deakin, and Schipper 2013) Provide Italy$$$ • Provide thematic maps for regions for information (Viola and Celauro 2015) engineers to select asphalt binder • Knowledge of statistical significance of temperature trends’ effects on pavements Long-term Australia$$$ Develop secondary routes especially in areas with planning (Taylor and Philp 2015) wetter climate predictions Source: Original table for this publication. Note: These strategies include forming forums and providing information to the planners. $$$ = high-income countries; $$ = middle-income countries; $ = low-income countries. References Daniel, J. S., J. M. Jacobs, E. Douglas, R. B. Mallick, and K. Hayhoe. 2014. “Impact of Climate Change on Pavement Performance: Preliminary Lessons Learned through the Infrastructure and Climate Network (ICNet).” Climatic Effects on Pavement and Geotechnical Infrastructure, edited by J. Liu, P. Li, X Zhang, and B. Huang, 1–9. https://doi.org/10.1061/9780784413326.001 Dawson, A. 2014. “Anticipating and Responding to Pavement Performance as Climate Changes.” In Climate Change, Energy, Sustainability and Pavements, edited by K. Gopalakrishnan, W. J. Steyn, and J. Harvey, 127–57. Berlin, Heidelberg: Springer. de Abreu, V. H. S., A. S. Santos, and T. G. M. Monteiro. 2022. “Climate Change Impacts on the Road Transport Infrastructure: A Systematic Review on Adaptation Measures.” Sustainability 14 (14): 8864. https://doi.org/10.3390/su14148864 Espinet, X., A. Schweikert, N. van den Heever, and P. Chinowsky. 2016. “Planning Resilient Roads for the Future Environment and Climate Change: Quantifying the Vulnerability of the Primary Transport Infrastructure System in Mexico.” Transport Policy 50: 78–86. https://doi.org/10.1016/j. tranpol.2016.06.003 Gudipudi, P. P., B. S. Underwood, and A. Zalghout. 2017. “Impact of Climate Change on Pavement Structural Performance in the United States.” Transportation Research Part D: Transport and Environment 57: 172–84. https://doi.org/10.1016/j.trd.2017.09.022 Knott, J. F., J. E. Sias, E. V. Dave, and J. M. Jacobs. 2019. “Seasonal and Long-Term Changes to Pavement Life Caused by Rising Temperatures from Climate Change.” Transportation Research Record 2673 (6): 267–78. https://doi.org/10.1177/0361198119844249 Kumlai, S., P. Jitsangiam, and P. Pichayapan. 2017. “The Implications of Increasing Temperature due to Climate Change for Asphalt Concrete Performance and Pavement Design.” KSCE Journal of Civil Engineering 21 (4): 1222–34. https://doi.org/10.1007/s12205-016-1080-6 Mallick, R. B., M. J. Radzicki, J. S. Daniel, and J. M. Jacobs. 2014. “Use of System Dynamics to Understand Long-Term Impact of Climate Change on Pavement Performance and Maintenance Cost.” Transportation Research Record 2455 (1). https://doi.org/10.3141/2455-01 McAndrews, C., E. Deakin, and L. Schipper. 2013. “Including Climate Change Considerations in Latin American Urban Transport Practices and Policy Agendas.” Journal of Environmental Planning and Management 56 (5): 674–94. https://doi.org/10.1080/09640568.2012.698584 Meagher, W., J. S. Daniel, J. Jacobs, and E. Linder. 2012. “Method for Evaluating Implications of Climate Change for Design and Performance of Flexible Pavements.” Transportation Research Record 2305 (1). https://doi.org/10.3141/2305-12 Mulholland, E. and L. Feyen. 2021. “Increased Risk of Extreme Heat to European Roads and Railways with Global Warming.” Climate Risk Management 34: 100365. https://doi.org/10.1016/j.crm.2021.100365 84 Appendix A. Road Pavements: Impacts and Mitigation Strategies Qin, Y. 2015. “A Review on the Development of Cool Pavements to Mitigate Urban Heat Island Effect.” Renewable and Sustainable Energy Reviews 52: 445–59. https://doi.org/10.1016/j.rser.2015.07.177 Schweikert, A., P. Chinowsky, K. Kwiatkowski, and X. Espinet. 2014. “The Infrastructure Planning Support System: Analyzing the Impact of Climate Change on Road Infrastructure and Development.” Transport Policy 35: 146–53. https://doi.org/10.1016/j.tranpol.2014.05.019 Stoner, A. M. K., J. S. Daniel, J. M. Jacobs, K. Hayhoe, and I. Scott-Fleming. 2019. “Quantifying the Impact of Climate Change on Flexible Pavement Performance and Lifetime in the United States.” Transportation Research Record 2673 (1). https://doi.org/10.1177/0361198118821877 Taylor, M. A. . and M. L. Philp. 2015. “Investigating the Impact of Maintenance Regimes on the Design Life of Road Pavements in a Changing Climate and the Implications for Transport Policy.” Transport Policy 41: 117–35. https://doi.org/10.1016/j.tranpol.2015.01.005 Viola, F. and C. Celauro. 2015. “Effect of Climate Change on Asphalt Binder Selection for Road Construction in Italy.” Transportation Research Part D: Transport and Environment 37: 40–47. https://doi. org/10.1016/j.trd.2015.04.012 85 Appendix A. Road Pavements: Impacts and Mitigation Strategies Appendix B Effects of Heat for Traffic Collision across Geographies Table B.1  Impacts on Pavements and Corresponding Magnitude of Impacts as Identified by Multiple Studies Temperature Country Location (paper) Method Metric Magnitude of impacts change United States$$$ Alabama Correlation Heatwave Traffic collision 1.4% insignificant decrease (Wu 2022) Continental Correlation Heatwave Collision risk 2.9% significant increase (Wu, Zaitchik, and Gohlke 2018) Maryland Correlation 1-day increase in Collision risk 1% insignificant increase (Liu et al. 2017) extreme weather Indiana Correlation Temperature Interstate accidents Positive correlation in summer (Rosselló and Saenz-de-Miera 2011) New York Regression 1°C rise Relative accident risk 1.58% increase over the 2 days (Hou et al. 2022) model following temperatures above 26.1°C Chicago, Los Angeles, Seattle Regression 1°C rise Relative accident risk Insignificant effects (Hou et al. 2022) model France$$$ (Bergel-Hayat et al. 2013) Regression 1°C rise Injury accidents 0.4% rise for main roads and 2% for model motorways Netherlands$$$ (Bergel-Hayat et al. 2013) Regression 1°C rise Injury accidents 2–3% rise for motorways and 1% for model rural roads (Hermans et al. 2006) Regression 10 minutes Number of crashes 5.7% increase model additional sunshine (Brijs, Karlis, and Wets 2008) Regression 1°C rise Number of crashes 1–1.2% increase model Greece$$$ Athens Correlation Temperature > 30°C Number of crashes 5% increase (Bergel-Hayat et al, 2013) Spain$$$ Catalonia Regression Heatwave days Risk of crashes 2.9% significant increase (Basagaña et al. 2015) model Catalonia Regression 1°C rise Risk of crashes with 1.1% significant increase (Basagaña et al. 2015) model driver performance factors Balearic Islands Regression Temperature Traffic crashes Insignificant effects (Rosselló and Saenz-de-Miera model 2011) Belgium$$$ (Van den Bossche, Wets, and Regression 1 hour increase Number of accidents 0.05% increase Brijs 2004) model in monthly sunny with light injury hours China$$ Shenzhen Correlation 1°C rise above 17°C Hourly road traffic 0.9% increase; 0.98% increase during (Zhan et al. 2020) casualties warm season; 1.18% increase during peak traffic hours Taipei City, Taiwan, China Regression 1°C rise Traffic accidents 0.8% increase; 0.9% increases for (Lin et al, 2015) model motorcycle accidents Shantou city Correlation Temperature Road traffic injuries Significant positive (Gao et al. 2016) 86 Heatwaves and Their Effects on Transportation Systems: A Comprehensive Review Temperature Country Location (paper) Method Metric Magnitude of impacts change China$$ Macao SAR, China Regression 1°C rise Number of mild Increase of 0.7 per 100,000 (Lio et al. 2019) model injuries population Kuwait$$$ (Al-Harbi, Yassin, and Shams Regression Temperature Accidents • Temperature most influential 2012) model meteorological condition • Correlations between 0.77 and 0.84 Iran$$ (Dastoorpoor et al. 2016) Correlation Temperature Road traffic accidents Significant positive Saudi Arabia$$$ (Nofal and Saeed 1997) Regression Temperature above Road Traffic Accidents More frequent in summer between model 42°C 12 and 3 p.m. Nordic Countries$$$ Norway Regression Additional 1 hour of Number of crashes 4% decrease (Fridstrøm et al. 1995) model daylight Denmark Regression Additional 1 hour of Number of crashes 0.6% decrease (Fridstrøm et al. 1995) model daylight Sweden Regression Additional 1 hour of Number of crashes 3.9% decrease (Fridstrøm et al. 1995) model daylight Pakistan$$ (Ali, Yaseen, and Khan 2020) Error correction 1% rise Road deaths 3.63% increase model Vehari Punjab (Suburban) Correlation Temperature Road traffic accidents Insignificant effects (Hammad et al. 2019) Tanzania$$ (Magesa et al. 2023) Regression Temperature Number of crashes Insignificant effects model South Africa$$ (Milford et al. 2016) Regression Temperature Motor vehicle Insignificant effects model collisions Nigeria$$ (Olawole 2016) Correlation Temperature Road traffic accidents Insignificant effects Italy $$$ (Gariazzo et al., 2021) Regression Hot temperature Risk of road crashes 10% increase; 21% increase for model motorcycles use South Korea$$$ Seoul-Incheon, Busan, Daegu, Regression 1°C rise above 30°C Overall accidents 0.59% increase Daejeon, and Gwangju model (Park, Choi, and Chae 2021) Japan$$$ Tokyo Regression 1 °C rise Motor vehicle Increase by 0.025 (Abe et al. 2008) model collisions Global (He et al. 2023) Regression High temperature Deaths of road injury • Increased by 8.5% between 1990 model and 2019 • Increase from 20,270 to 28,396 Age-standardized • Increased by 13.2% between 1990 disability-adjusted life and 2019 years • Increased from 1,169,309 to 1,414,527 Africa$ (He et al. 2023) Regression High temperature Age-standardized 32.29 disability life years lost per model disability-adjusted life 100,000 people years Age-standardized 0.74 deaths per 100,000 people mortality rates India$$ (He et al. 2023) Regression High temperature Number of deaths Highest number of deaths in the model world (10,020) Nigeria$$ (He et al. 2023) Regression High temperature Number of deaths 2nd highest number of deaths in the model world (1,682) Brazil$$ (He et al. 2023) Regression High temperature Number of deaths 3rd highest number of deaths in the model world (1,294) 87 Appendix B. Effects of Heat for Traffic Collision across Geographies Temperature Country Location (paper) Method Metric Magnitude of impacts change Oman$$ (He et al. 2023) Regression High temperature Age-standardized Highest rate: 5.93 deaths per 100,000 model mortality rates people United Arab (He et al. 2023) Regression High temperature Age-standardized Highest rate: 5.36 deaths per 100,000 Emirates (UAE) $$$ model mortality rates people Burkina Faso$ (He et al. 2023) Regression High temperature Age-standardized Highest rate: 3.62 deaths per 100,000 model mortality rates people Iceland$$$, (He et al. 2023) Regression High temperature Number of deaths Lowest number of deaths Greenland$$$, model Malta$$$ Source: Original table for this publication. Note: $$$ = high-income countries; $$ = middle-income countries; $ = low-income countries. References Abe, T., Y. Tokuda, S. Ohde, S. Ishimatsu, T. Nakamura, and R. B. 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Yand, B. Chen, and W. Hu. 2022. “Ambient Temperatures Associated with Increased Risk of Motor Vehicle Crashes in New York and Chicago.” Science of The Total Environment 830:154731. https://doi.org/10.1016/j.scitotenv.2022.154731 Lin, L. W., H. Y. Lin, C. Y. Hsu, H. H. Rau, and P. L. Chen. 2015. “Effect of Weather and Time on Trauma Events Determined Using Emergency Medical Service Registry Data.” Injury 46 (9): 1814–20. https://doi. org/10.1016/j.injury.2015.02.026 Lio, C., H. H. Cheong, C. H. Un, I. L. Lo, and S. Y. Tsai. 2019. “The Association between Meteorological Variables and Road Traffic Injuries: A Study from Macao”. PeerJ. 7: e6438. https://doi.org/10.7717/ peerj.6438 Liu, A., S. I. Soneja, C. Jiang, C.Huang, T. Kerns, K. Beck, C. Mitchell, and A. Sapkota. 2017. “Frequency of Extreme Weather Events and Increased Risk of Motor Vehicle Collision in Maryland.” Science of The Total Environment 580: 550–55. https://doi.org/10.1016/j.scitotenv.2016.11.211 Magesa, G., E. E. Sinkwembe, N. Shaban, and T. Ngailo. 2023. “Bivariate Discrete Time Series Model for Assessing the effects of Rainfall and Temperature on Road Accidents: The Case of Morogoro and Pwani Regions in Tanzania.” Scientific African 19: e01522. https://doi.org/10.1016/j.sciaf.2022.e01522 Milford, K. L., P. H. Navsaria, A. J. Nicol, and S. Edu. 2016. “Trauma Unit Attendance: Is There a Relationship with Weather, Sporting Events and Week/Month-End Times? An Audit at an Urban Tertiary Trauma Unit in Cape Town.” South African Journal of Surgery 54 (4): 22–27. https://pubmed.ncbi.nlm.nih. gov/28272852/ Nofal, F. H. & Saeed, A. A. W., 1997. “Seasonal Variation and Weather Effects on Road Traffic Accidents in Riyadh City.” Public Health 111 (1): 51–55. https://doi.org/10.1038/sj.ph.1900297 Olawole, M. O.,2016. “Impact of Weather on Road Traffic Accidents in Ondo State, Nigeria: 2005-2012.” Analele Universitatii din Oradea, Seria Geografie. https://geografie-uoradea.ro/Reviste/Anale/Art/2016- 1/4.AUOG_697_Moses.pdf Park, J., Y. Choi, and Y. Chae. 2021. “Heatwave Impacts on Traffic Accidents by Time-of-Day and Age of Casualties in Five Urban Areas in South Korea.” Urban Climate 39: 100917. https://doi.org/10.1016/j. uclim.2021.100917 Rosselló, J. and O. Saenz-de-Miera. 2011. “Road Accidents and Tourism: The Case of the Balearic Islands (Spain).” Accident Analysis & Prevention 4 (3): 675–83. https://doi.org/10.1016/j.aap.2010.10.011 Van den Bossche, F., G. Wets, and T. Brijs. 2007. “A Regression Model with ARIMA Errors to Investigate the Frequency and Severity of Road Traffic Accidents.” Steunpunt Verkeersveiligheid Research Publications. http://hdl.handle.net/1942/4543 Wu, C. 2022. 2022. “Heat Waves and Road Traffic Collisions in Alabama, United States.” Annals of the American Association of Geographers 112 (5): 1313–27. https://doi.org/10.1080/24694452.2021.1960145 Wu, C. Y., B. F. Zaitchik, and J. M. Gohlke. 2018. “Heat Waves and Fatal Traffic Crashes in the Continental United States.” Accident Analysis & Prevention 119: 195–201. https://doi.org/10.1016/j.aap.2018.07.025 Zhan, Z. Y., Y. M. Yu, T. T. Chen, L. J. Xu, and . Q. Ou. 2020. “Effects of Hourly Precipitation and Temperature on Road Traffic Casualties in Shenzhen, China (2010–2016): A Time-Stratified Case-Crossover Study.” Science of The Total Environment 720: 137482. https://doi.org/10.1016/j. scitotenv.2020.137482 89 Appendix B. Effects of Heat for Traffic Collision across Geographies Appendix C Railways Impacts and Mitigation Strategies Table C.1  Impacts of Heat on Railways and Corresponding Magnitude of Impacts as Identified by Different Studies Prediction year/ Impact Country (paper) Method Temperature Details / Magnitude of impacts rise Buckling of rails Europe$$$ CWR-SAFE model 4°C rise • Factors affecting buckling: Rail size, lateral resistance, (Mulholland and ballast friction coefficient, resistance, track curvature, Feyen 2021) foundation modulus, and axle load • 85% damages to conventional rails and 15% to high-speed rails • Low curvature lines are vulnerable Spain$$$ Monte Carlo simulation 2050s • Increase from 20 to up to 500 in number of buckling (Sanchis et al. 2020) events • Northern and coastal sections have low sensitivity United States$$$ Infrastructure Planning 2100 • Rail expansion up to 1 inch with 10°C increase (Chinowsky et al. Support System (IPSS) • Greatest impacts in areas of high rail network density, low 2019) SFT, and high temp rise. Train delays United Kingdom$$$ Regression 2000s Weather adversities responsible for up to 20% of unplanned (Thornes and Davis delays 2002) United Kingdom$$$ Threshold temperature 2040s • Speed restrictions to 20-–30 mph based on track (Palin et al. 2013) properties • Increase from 10–20% to 30% times for speed restriction conditions in some regions Scotland$$$ Threshold temperature 2040s A speed restriction will be implemented twice (Palin et al. 2013) United States$$$ Infrastructure Planning 2100 $103–$138 billion cumulative projected cost based on delay- (Chinowsky et al. Support System (IPSS) minutes 2019) Overhead Line United Kingdom$$$ Threshold temperature 2040s Sagging occurs when air temperature is around 33°C Equipment (OLE) (Palin et al. 2013) sagging A 7-fold increase in days that sagging occurs in southwest United Kingdom Ballast maintenance United Kingdom$$$ Threshold temperature 2040s Twice the number of days that work is not possible, with (Palin et al. 2013) number of days up to 40% Scotland$$$ Threshold temperature 2040s Three times the number of days that work is not possible (Palin et al. 2013) Staff exposure United Kingdom$$$ Threshold temperature 2040s A 3- to 8-fold increase in heat stress episodes (25–150 days) (Palin et al. 2013) in the southern United Kingdom Ventilation issues United Kingdom$$$ Review n.a. • 11°C above the ambient temperature for underground (Baker et al. 2010) station • Temperature range for comfort: 21°C–26°C in trains; 17°C –25°C in stations 90 Heatwaves and Their Effects on Transportation Systems: A Comprehensive Review Prediction year/ Impact Country (paper) Method Temperature Details / Magnitude of impacts rise Economic Impacts Europe$$$ CWR-SAFE model 4°C rise €1.5 billion (€3,004/kilometer) increase in annual O&M costs (Mulholland and €0.1 billon annual cost when mitigating climate change to a Feyen 2021) 1.5°C scenario Germany$$$ CWR-SAFE model 4°C rise € 882 million (€ 9,284/kilometer) increase in annual O&M (Mulholland and costs Feyen 2021) Source: Original table for this publication. Note: CWR-SAFE = Continuous Welded Rail – Safety Model; n.a. = not applicable; O&M = operations and maintenance; SFT = Stress Free Temperature; $$$ = high- income countries; $$ = middle-income countries; $ = low-income countries. Table C.2  Mitigation Strategies for Impacts on Rail Transport Due to Heatwaves. Strategy Country (paper) Details / Strategy effectiveness Speed Restrictions Europe $$$ Reducing the speed limit of a train (Mulholland and Feyen 2021) Spain$$$ Speed restrictions imposed when certain temperature thresholds are passed (Sanchis et al. 2020) United Kingdom$$$ • Speed restricted to 20–30 miles per hour (Palin et al. 2013) • Variations in speed restrictions and temperature threshold based on track bed and ballast properties United States$$$ Reduce traffic on affected areas by reducing speed or stopping train completely (Chinowsky et al. 2019) Issues: Delay in rail traffic; decreased speeds may increase buckling North America$$$ Speed restrictions vary for service provider and service type (passenger / freight) (Changnon 2013) United Kingdom$$$ Actions taken: (Network Rail 2025) • East Coast Main Line closed in 2022 • Thameslink and Great Northern services canceled • Euston and London Marylebone service limited Sensors United States$$$ Measuring temperature (Chinowsky et al. 2019) • Apply targeted speed restrictions (small rail sections and times) • Reduces cost from $103–$138 billion to $4–$29 billion Sensors: Greatest initial impact and scope for near-term advance rail defect monitoring Spain$$$ Early warning systems of extreme temperatures (Sanchis et al. 2020) United Kingdom$$$ Currently placed watchman to monitor track may be replaced by sensors (Palin et al. 2013) United Kingdom$$$ Forecasting and monitoring weather and track temperature (Network Rail 2025) Planning Europe$$$ Setting regional SFTs based on projected future temperatures (Mulholland and Feyen 2021) Spain$$$ Higher SFTs are required (Sanchis et al. 2020) United Kingdom$$$ High SFT (Palin et al. 2013) • Benefit; Decreases buckling risks at high temperatures • Issue: Increases cracking / breaking risks at low temperature Australia and the United States$$$ Higher range of SFTs are applied (Palin et al. 2013) 91 Appendix C. Railways Impacts and Mitigation Strategies Strategy Country (paper) Details / Strategy effectiveness Planning Germany$$$ Replace traditional ballasted track with sleepers with continuous concrete slab track on high-speed (Palin et al. 2013) lines • Benefit: Requires less maintenance • Issue: Generates more noise United Kingdom$$$ Seasonal stressing regime for re-stressing rails for winter and summer is better (Dobney et al. 2009) United Kingdom$$$ Raise the SFT during routine track renewals (Baker et al. 2010) United States$$$ Changes in track design are long term and expensive in short/mid term (Chinowsky et al. 2019) Track adaptation Spain$$$ Coatings and paints reduce average rail temperature gain (Sanchis et al. 2020) United Kingdom$$$ White paint on the hottest rails to reduce temperatures (Network Rail 2025) Other United Kingdom$$$ Install specialized weights to prevent overhead lines from sagging (Network Rail 2025) Source: Original table for this publication. Note: Speed restrictions and use of sensors are the most common approaches performed by the practitioners. SFT = stress-free temperature; $$$ = high-income countries; $$ = middle-income countries; $ = low-income countries. References Baker, C. J., L. Chapman, A. Quinn, and K. Dobney. 2010. “Climate Change and the Railway Industry: A Review.” Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 224 (3). https://doi.org/10.1243/09544062JMES1558 Changnon, S. 2013. Railroads and Weather: From Fogs to Floods and Heat to Hurricanes, the Impacts of Weather and Climate on American Railroading. American Meteorological Society. Chinowsky, P., J. Helman, S. Gulati, J. Neumann, and J. Martinich. 2019. “Impacts of Climate Change on Operation of the US Rail Network.” Transport Policy 75: 183–91. https://doi.org/10.1016/j. tranpol.2017.05.007 Dobney, K., C. J. Baker, A. D. Quinn, and L. Chapman. 2009. “Quantifying the Effects of High Summer Temperatures Due to Climate Change on Buckling and Rail Related Delays in South‐East United Kingdom.” Meteorological Applications 16 (2): 245–51. https://doi.org/10.1002/met.114 Mulholland, E. and L. Feyen. 2021. “Increased Risk of Extreme Heat to European Roads and Railways with Global Warming.” Climate Risk Management 34: 100365. https://doi.org/10.1016/j.crm.2021.100365 Network Rail. 2025. Hot Weather and the Railway. https://www.networkrail.co.uk/campaigns/hot- weather-and-the-railway/ Palin, E. J., H. E. Thornton, C. T. Mathison, R. E. McCarthy, R. T. Clark, and J. Dora. 2013. “Future Projections of Temperature-Related Climate Change Impacts on the Railway Network of Great Britain.” Climatic Change 120: 71–93. https://doi.org/10.1007/s10584-013-0810-8 Sanchis, I. V., R. I. Franco, P. S. Zuriaga, and P. M. Fernández. 2020. “Risk of Increasing Temperature due to Climate Change on Operation of the Spanish Rail Network.” Transportation Research Procedia 45: 5–12. https://doi.org/10.1016/j.trpro.2020.02.056 Thornes, J. E. and B. W. Davis. 2002. “Mitigating the Impact of Weather and Climate on Railway Operations in the UK.” Paper presented at the ASME/IEEE Joint Railroad Conference. Washington, DC, June 2002. https://doi.org/10.1109/RRCON.2002.1000089 92 Appendix C. Railways Impacts and Mitigation Strategies Appendix D Air Transportation Impacts and Mitigation Strategies Table D.1  Impacts on Airports and Corresponding Magnitude of Impacts as Identified by Multiple Studies Prediction Impact Country (paper) Method Magnitude of impacts year Runway surface Europe$$$ EUROCONTROL a n.a. Extreme temperatures exceed design standards, which leads melting (Burbidge 2016) to damage to tarmac surfaces and runways / aprons (surface melting). Slovakia$$$ Measurements n.a. Slab surface temperature was 56.4℃ at an air temperature of 34℃. (Hodáková et al. 2019) HVAC system United States$$$ Review 2080s Armstrong New Orleans International Airport: (Thompson 2016) • 2040s: Increase in cooling needs = decrease in heating needs. • 2080s: Cooling needs increase (40%) > heating needs decrease (20%) compared to 2010s. Europe$$$ EUROCONTROL n.a. Increased summer cooling. (Burbidge 2016) Reduced takeoff Global Assess weight restrictions 2080s • Approximately 100-foot increase in mean airport density altitude weights (Coffel, Thompson, with 1°C rise. and Horton 2017) • Airports with short runways and high temperatures or those at high elevations experience the largest impacts. • Large aircraft (such as the Boeing 777-300 and Boeing 787-8) have the greatest impacts (30–40% flights). United States$$$ Assess weight restrictions 2080s At New York LaGuardia, Boeing 737-800 weight-restricted 50% time (Coffel, Thompson, with reductions of up to 3.5% of payload capacity. and Horton 2017) Dubai$$$ Assess weight restrictions 2080s At Dubai (DXB), Boeing 777-300 weight-restricted about 55% time (Coffel, Thompson, with reductions of up to 6.5% of payload capacity. and Horton 2017) Noise impacts Global Review n.a. Changes in noise impacts due to changes in power settings, (Thompson 2016) ground roll, and climb performance. Fire hazard Global Review n.a. Flash point of aviation fuel (38°C) may be exceeded on hot days. (Thompson 2016) Interconnected Global Review n.a. Connected transportation networks such as highways, rail lines, network (Thompson 2016) and tunnels should also be considered. Staff health issues Europe$$$ EUROCONTROL n.a. Overheating of equipment and health issues for staff are common. (Burbidge 2016) Source: Original table for this publication. Note: Reduced takeoff weights and runway surface melting are commonly identified impacts. EUROCONTROL is the European Organization for the Safety of Air Navigation. HVAC = heating, ventilation, and air conditioning; n.a. = not applicable. $$$ = high-income countries; $$ = middle-income countries; $ = low-income countries. 93 Heatwaves and Their Effects on Transportation Systems: A Comprehensive Review Table D.2  Mitigation Strategies for Impacts on Air Transportation Due to Heatwaves Strategy Country (paper) Details / Strategy effectiveness Weight restrictions Global • Non-trivial cost on airlines (Coffel, Thompson, • Reduced payload (passengers and cargo) and Horton 2017) Global Most direct solution to operational issues (Thompson 2016) Flight operations Global Reschedule flights, especially those with high TOWs, to cooler (Coffel, Thompson, hours of the day and Horton 2017) Planning Global Adaptation in aircraft design, airline schedules, and/or runway (Coffel, Thompson, lengths. and Horton 2017) Issue: Expensive and politically difficult Global Lengthening runway (Thompson 2016) Issue: Expensive, needs additional space, environmental concerns of noise and air quality Source: Original table for this publication. Note: Weight restriction is the most common approach performed by the practitioners. TWO = takeoff weight. References Burbidge, R. 2016. “Adapting European Airports to a Changing Climate.” Transportation Research Procedia 14 (2016): 13–23. https://doi.org/10.1016/j.trpro.2016.05.036 Coffel, E. D., T. R. Thompson, and R. M. Horton. 2017. “The Impacts of Rising Temperatures on Aircraft Takeoff Performance.” Climatic Change 144: 381–88. https://doi.org/10.1007/s10584-017-2018-9 Hodáková, D., A. Zuzulová, S. Cápayová, and T. Schlosser. 2019. “Safety of Air Transport in Relation to Pavement Condition of Runways.” Transportation Research Procedia 43: 300–08. https://doi. org/10.1016/j.trpro.2019.12.045 Thompson, T. R. 2016. Climate Change Impacts upon the Commercial Air Transport Industry: An Overview.” Carbon & Climate Law Review 10 (2): 105–12. https://www.jstor.org/stable/44135213 94 Appendix D. Air Transportation Impacts and Mitigation Strategies Appendix E Public Transportation Impacts and Mitigation Strategies Table E.1  Impacts on Public Transit and the Corresponding Magnitude of Impacts Impact Country (paper) Method Prediction year Details / Magnitude of impacts Reduced United Kingdom$$$ Review — Especially observed within the vehicles comfort (BBC News 2025) Global Experiment — Sultry and uncomfortable sensation with conventional bus stops (Montero-Gutiérrez retaining heat and humidity et al. 2023) United States$$$ Surveys and 2019 50% of participants felt hot or very hot (Dzyuban et al. 2022) temperature sensors 55% felt thermally uncomfortable United States$$$ - — High exposure and long wait times in areas with low residential (Fraser and Chester density, irregular street networks, and transit routes are not 2017) directly connected to major activity centers United States$$$ Review — In Los Angeles, 25% of bus stops have shelters (Turner, Middel, and Vanos 2023) Reduced United Kingdom$$$ Implemented — Sharp drop in passengers observed on hottest day in July 2022 Ridership (TfL 2022) technology (people decided to work from home) United States$$$ Regression model Maximum • Statistically significant decrease of 0.3% (Ngo 2019) temperature > 85°F • High decrease for low bus frequency areas (90th percentile) China$$ Regression model — • Nonlinear relation of temperature and ridership (Inverted U (Wu and Liao 2020) with peak at 24°C) • 50% trips affected: leisure and shopping activities; 23% trips affected: work; 15% trips affected: education-based • Buses are less attractive than subway United States$$$ Regression model — 1.7% decrease in ridership with bus stops without trees (Lanza and Durand 2021) United States$$$ Regression model Temperature > 23°C 0.4% lower ridership for unsheltered bus stops (Miao, Welch, and Sriraj 2019) Other Impacts United Kingdom$$$ Review — Reliability of electronic sensors decrease (McGuire et al. 2025) United States$$$ Surveys and 2019 High temperature of sun-exposed surfaces (Dzyuban et al. 2022) temperature sensors • Temperatures exceed skin burn thresholds • Metal bench seats’ temperature up to between 39.7°C and 50°C Ireland$$$ Regression model 2019 Increased bus journey times for both buses in dedicated lanes (French and and buses in mixed traffic O’Mahony 2021) Source: Original table for this publication. Note: Reduced comfort and reduced ridership of public transit users are the two major impacts. — = not available; $$$ = high-income countries; $$ = middle-income countries; $ = low-income countries. 95 Heatwaves and Their Effects on Transportation Systems: A Comprehensive Review Table E.2  Structural Mitigation Strategies for Reduced Trips on Public Transit Due to Extreme Heat Strategy Country (paper) Details / Strategy effectiveness Shade / Global 20°C–40°C decrease in net heat burden in shade compared to nearby sun-exposed shelter (Turner, Middel, and Vanos areas in arid and tropical climates 2023) United States$$$ • Shelters: No significant change in ridership (Lanza and Durand 2021) • 1% increase in tree canopy: Less decrease (1.6%) in ridership than areas with no trees (1.7%) Spain$$$ Installed climate shelters with shaded areas and water sprinkler starting 2018 in (Montero-Gutiérrez, et al., 2023) Barcelona Global Shade and reflective materials (Montero-Gutiérrez, et al., 2023) • Gain: Decreased radiation • Loss: Does not improve the thermal sensation of occupants in extreme temperature and humidity Malaysia$$ Opaque concrete-based tile roof better than translucent plastic roof of white (Goshayeshi et al. 2013) polycarbonate in terms of temperature, humidity, mean radiant temperature, and thermal perception United States$$$ Presence of trees enables: (Dzyuban et al. 2022) • Up to 19°C reduction in physiological equivalent temperature (PET) • Up to 16°C reduction in surface temperatures • Cooling from trees is equivalent to that from shade structures United States$$$ Los Angeles Department of Transportation installed Shade La Sombrita (May 2023) (Jiménez and Albeck-Ripka, • Positives: Metal bus shelters, small and quick to install 2023) • Issues: Costs $10,000 each, but does not provide sufficient shade for even two people United States$$$ Austin’s Capital Metro Conditions for a bus stop shelter: (Lanza and Durand 2021) • Generated based on number of daily boardings • Close to high-activity areas United States$$$ • Weather-proof attributes help retain and attract ridership on extreme weather days (Miao, Welch, and Sriraj 2019) • Effect of shelters is more pronounced on weekdays, and for stops with lower service frequency and fewer transfers. Sensors United Kingdom$$$ Monitoring climate conditions to improve passenger comfort (TfL 2023) Spain$$$ Smart ventilation regulation (RESPIRA® control system) for metro: (TMB and SENER 2020) • Measures and predicts the environmental conditions inside stations to apply operations to fans • Lowers heat index of passengers and staff Cooling Spain$$$ In March 2019, a 1.2°C temperature reduction was obtained by changing ventilation Panels (TMB and SENER 2020) setpoints in Barcelona. United Kingdom$$$ 10°C–15°C temperature reduction was obtained with cooling panels in trials at Holborn (TfL 2022) station in July 2022 (circulating cold water around pipework and industrial-sized fan) France$$$ “Cool oases” in public spaces were implemented in Paris in 2017. These consisted of: (Montero-Gutiérrez et al. 2023) • Shaded areas with a water mist system and fountains • A cool, damp atmosphere Global Cooling techniques with renewable energy (Montero-Gutiérrez et al. 2023) • Design: Radiant system in shelter with low-temperature water circulation, solar powered for self-sufficiency • Effects: Drops from 40°C to 18°C–20°C in surface temperature within 20 minutes, reduced thermal loads (100 to 50–70 watts per square meter Kazakhstan$$ • Design: Walls and roof of radiative cooling panels (RCPs) (Alikhanova et al. 2019) • Effects: Up to a 10°C reduction in Universal Thermal Climate Index (UTCI) 96 Appendix E. Public Transportation Impacts and Mitigation Strategies Strategy Country (paper) Details / Strategy effectiveness Vehicles United Kingdom$$$ Air-conditioned trains to replace the Piccadilly line (underground) train (by 2025) (TfL 2022) United States$$$ Prepare spare vehicles for deployment during extreme heat events (Rosenthal et al. 2022) Operations United States$$$ Rerouting of bus services (Rosenthal et al. 2022) • Minimize wait time and heat exposure • Rerouting 10% of the fleet reduced network-wide exposure by 35% Source: Original table for this publication. Note: Shade and shelter-based approaches, along with cooling panels and sensors, are a few of the approaches discussed in the literature. $$$ = high-income countries; $$ = middle-income countries; $ = low-income countries. Table E.3  Non-Structural Mitigation Strategies for Reduced Public Transportation Trips Strategy Country (paper) Details / Strategy effectiveness Climate United Kingdom$$$ Resilience task force launched Officer (Network Rail 2025) United States$$$ • Adaptable workforce: Training drivers for various routes (Rosenthal et al. 2022) • Negotiating flexible work arrangements Travel United Kingdom$$$ • Provide public travel advice announcements, from “Travel only if necessary” to “Do Advice (Network Rail 2025) not travel” • Reminding everyone to drink water and carry refillable water bottles Hydration United Kingdom$$$ • Provide free cold-water refill fountains at railway stations (Network Rail 2025) • Provide free ice creams at stations United States$$$ • Drinking fountains beneficial for 33%+ respondents (Dzyuban et al. 2022) • Misters, additional vegetation, shade, and water fountains result in perceived cooling benefits United States$$$ People generally have the habit of staying hydrated and wearing a hat (Lanza and Durand 2021) Aesthetics United States$$$ • Artistic elements, trees, and vegetated trellises mean that stops are rated as cooler and (Dzyuban et al. 2022) • Electric plugs, Wi-Fi, or real-time information at stops reduce perceived wait time Facilities Source: Original table for this publication. Note: These strategies include appointing a climate officer and hydration facilities for travelers. $$$ = high-income countries; $$ = middle- income countries; $ = low-income countries. References Alikhanova, A., A. Kakimzhan, A. Mukhanov, and L. Rojas-Solórzano. 2019. “Design of A Bus Shelter Based on Green Energy Technologies for Extreme Weather Conditions in Nur-Sultan, Kazakhstan.” Sustainable Energy Technologies and Assessments 36: 10054. https://doi.org/10.1016/j.seta.2019.100544 BBC News. 2025. “London Bus Heat Complaints Highest on Record.” BBC News, August 8, 2025. https:// www.bbc.com/news/articles/cvgnp92k2zro Dzyuban, Y., D. M. Hondula, J. K. Vanos, A. Middel, P. J. Coseo, E. R. Kuras, and C. L. Redman. 2022. “Evidence of Alliesthesia during a Neighborhood Thermal Walk in a Hot and Dry City.” Science of The Total Environment 834: 155294. https://doi.org/10.1016/j.scitotenv.2022.155294 97 Appendix E. Public Transportation Impacts and Mitigation Strategies Fraser, A. M. and M. V. Chester. 2017. “Transit System Design and Vulnerability of Riders to Heat.” Journal of Transport & Health 4: 216–25. https://doi.org/10.1016/j.jth.2016.07.005 French, C. and M. O’Mahony. 2021. “Using Automatic Vehicle Location System Data to Assess Impacts of Weather on Bus Journey Times for Different Bus Route Types.” Paper presentend at the IEEE International Intelligent Transportation Systems Conference (ITSC), Indianapolis, IN, USA, 2021, 2137–44. https://doi.org/10.1109/ITSC48978.2021.9564546 Goshayeshi, D., M. Zaky Jaafar, M. Fairuz Shahidan, and F. Khafi. 2013. “Thermal Comfort Differences between Polycarbonate and Opaque Roofing Material Installed in Bus Stations of Malaysia.” European Online Journal of Natural and Social Sciences 2 (3): 379–93. https://european-science.com/eojnss/article/ view/114/pdf Jiménez, J. and L. Albeck-Ripka. 2023. “L.A.’s Bus Stops Need Shade. Instead, They Got La Sombrita.” The New York Times, May 25, 2024. https://www.nytimes.com/2023/05/25/us/la-sombrita-bus-los-angeles. html Lanza, K. and C. Durand. 2021. “Heat-Moderating Effects of Bus Stop Shelters and Tree Shade on Public Transport Ridership.” International Journal of Environmental Research and Public Health 18 (2): 463. https://doi.org/10.3390/ijerph18020463 McGuire, C., Y. Naderi, A. Gardner, M. Sharma, L. Solanki, O. Jenssen, B. Page, F. Long, M. Adams, C. Evangelides, N. Hamilton, and R. Hogarth. 2025. Impacts on Energy Assets from Extreme Heat and Heatwaves: Final Report. Commissioned by the UK Department for Energy Security and Net Zero. https://assets.publishing.service.gov.uk/media/680b9d79521c5b6f2883cca1/impacts-on-energy-assets- from-extreme-heat-and-heatwaves.pdf Miao, Q., E. W. Welch, and P. S. Sriraj. 2019. ”Extreme Weather, Public Transport Ridership and Moderating Effect of Bus Stop Shelters.” Journal of Transport Geography 74: 125–33. https://doi. org/10.1016/j.jtrangeo.2018.11.007/ Montero-Gutiérrez, P., J. Sánchez Ramos, MC. Guerrero Delgado, A. Cerezo-Narváez, T. Palomo Amores, and S. Álvarez Domínguez, 2023. “Natural Cooling Solution for Thermally Conditioning Bus Stops as Urban Climate Shelters in Hot Areas: Experimental Proof of Concept.” Energy Conversion and Management 296: 117627. https://doi.org/10.1016/j.enconman.2023.117627 Network Rail. 2025. Hot Weather and the Railway. https://www.networkrail.co.uk/campaigns/hot- weather-and-the-railway/ Ngo, N. 2019. “Urban Bus Ridership, Income, and Extreme Weather Events.” Transportation Research Part D: Transport and Environment 77: 464–75. https://doi.org/10.1016/j.trd.2019.03.009 Rosenthal, N., M. Chester, A. Fraser, D. M. Hondula, and D. P. Eisenman. 2022. “Adaptive Transit Scheduling to Reduce Rider Vulnerability during Heatwaves.” Sustainable and Resilient Infrastructure 7 (6): 744–55. https://doi.org/10.1080/23789689.2022.2029324 TfL (Transport for London). 2022. “TfL Trials Innovative Cooling Solution Designed to Reduce Temperatures on the Tube Network.” Press Release, July 22, 2022. https://tfl.gov.uk/info-for/media/ press-releases/2022/july/tfl-trials-innovative-cooling-solution-designed-to-reduce-temperatures-on-the- tube-network TfL (Transport for London). 2023. Climate Change Adaptation Plan 2023. https://content.tfl.gov.uk/tfl- climate-change-adaptation-plan.pdf TMB (Transports Metropolitans de Barcelona) and SENER. 2020. “The Barcelona Metro Implements Smart Ventilation Control to Prevent Infection.” Press Release, June 30, 2020. https://noticies.tmb.cat/ file/14464/download?token=Yjy2Hy3I Turner, V. K., A. Middel, and J. K. Vanos. 2023. “Shade Is an Essential Solution for Hotter Cities.” Nature 619: 694–97. https://doi.org/10.1038/d41586-023-02311-3 Wu, J. and H. Liao. 2020. “Weather, Travel Mode Choice, and Impacts on Subway Ridership in Beijing.” Transportation Research Part A: Policy and Practice 135: 264–79. https://doi.org/10.1016/j.tra.2020.03.020 98 Appendix E. Public Transportation Impacts and Mitigation Strategies Appendix F Active Transportation Impacts and Mitigation Strategies Table F.1  Impacts on Active Transport and Corresponding Magnitude of Impacts as Identified by Multiple Studies Threshold Impact Country (paper) Method Details / Magnitude of impacts temperatures Reduced Demand Canada$$$ Regression model 28°C Negatively affect cycling in Montreal (Miranda-Moreno and Nosal 2011) Canada$$$ Regression model n.a.. Parabolic effect of temperature on the number of pedestrians (Aultman-Hall, Lane, and Lambert 2009) Singapore$$$ Logit model 30.4°C • Cyclists: Work/school purposes: transfer to other modes; (Meng et al.2016) Leisure purposes: postpone the trips • 57.4% of cyclists will switch traffic mode, 80% of them taking a bus at the nearest bus stop if extreme weather is encountered en-route Netherlands$$$ Regression model n.a. Leisure trips are more weather-sensitive than commuter trips (Helbich, Böcker, and Dijst 2014) Netherlands$$$ Logit / Tobit model Temperature: • Cycling trips occur in the morning or evening of hot days (Böcker and Thorsson 24°C • Parabolic relationship between temperature and modal 2014) MRT: 52°C split for cycling observed PET: 30°C • Bell-shaped effect for bicycle demand and duration with temperature • Negative and significant effects for walking United States$$$ Regression model 24°C Reduced cycling in Portland, Oregon (Ahmed et al. 2012) Australia$$$ Regression model 28°C Reduced cycling in Melbourne (Phung and Rose 2007) United States$$$ Regression 90°F Decrease in counts above threshold (Lewin 2011) Netherlands$$$ Logit / Tobit model 25°C Bell-shape effect of temperature on bicycle usage (Sabir 2011) Reduced Comfort Australia$$$ Google Street View 2019 • Relatively little shade and lower comfort on streets next to (Sun et al. 2021) images single-level buildings • Reduced comfort on streets in urban areas (which have shorter trees and wider roads) Singapore$$$ Logit model 30.4°C Cyclists prefer lower temperature and lower humidity (Meng M. , Zhang, Wong, & Au, 2016) Netherlands$$$ Logit / Tobit model 25°C–30°C • Currently, 24 days of optimal temperature exceedance (Bröde et al. 2012) • By 2050, 30–47 days of optimal temperature exceedance 99 Heatwaves and Their Effects on Transportation Systems: A Comprehensive Review Threshold Impact Country (paper) Method Details / Magnitude of impacts temperatures Increased Risk Singapore$$$ Logit model 30.4°C • Elevated risk perception above the threshold perceptions (Meng et al. 2016) • Slow response time of cyclists United States$$$ Surveys -— Cyclists with higher skills and greater experience are less (Motoaki and Daziano affected by adverse weather 2015) United States$$$ Regression 30°C In San Francisco, the greatest frequency of cyclist-risky days (Mislan, Wethey, and occurs in May Helmuth 2009) Source: Original table for this publication. Note: Studies have assessed how the demand of active transport drops along with corresponding reduction in comfort. — = not available; $$$ = high- income countries; $$ = middle-income countries; $ = low-income countries. Table F.2  Mitigation Strategies for Decreased Active Transportation Trips Due to Heat Strategy Country (paper) Details / Strategy effectiveness Shade Australia’s Shade-creation policy $$$ Providing shade along cycleways and in parks, playgrounds, and outdoor dining areas (Queensland Health 2010) using trees, roofs, and shade structures Abu Dhabi Public Realm Design • Continuous shade for 80% of primary and 60% of secondary walkways Manual$$$ • Shaded rest areas at regular intervals (Abu Dhabi Urban Planning Council • 100% shade coverage for all formal play structures in public parks 2011) Israel$$$ Tel Aviv’s Shade Planning Guidelines: (Whiting 2023) • Continuous shade on 80% of public streets, paths, and walkways • 50% shade in school playgrounds United States$$$ Maricopa County in Arizona: (Turner, Middel, and Vanos 2023) • “Thermally Comfortable Pedestrian Route” should have a minimum of 20% shade coverage • Phoenix: Originally called for 25% increase in tree canopy (Tree and Shade Master Plan, 2010); modified in 2025 to take a more targeted approach Singapore$$$ At least 50% of public spaces and seating are shaded at 9 a.m., noon, and 4 p.m. in (Turner, Middel, and Vanos 2023) midsummer United States$$$ Providing opportunities for hydration, shade, and parks (Karner, Hondula, and Vanos 2015) Singapore$$$ Up to 4.5ºC temperature reduction due to shading (Chàfer et al. 2022) 100 Appendix F. Active Transportation Impacts and Mitigation Strategies Strategy Country (paper) Details / Strategy effectiveness Trees and vegetation United Kingdom$$$ Positives: (Kubilay et al. 2021) • Improves thermal comfort by shading and evapotranspiration • Reduction by up to 7°C in UTCI with cooling provided by trees Negatives: • Too dense vegetation decreases the ventilation because it blocks the wind Australia$$$ Tree-planting programs and increasing the shade along travel routes are effective (Sun et al. 2021) Singapore$$$ • Up to a 4ºC temperature reduction due to greenery during the day (Chàfer et al. 2022) • Up to a 1ºC temperature reduction with presence of vegetation during the night • Air temperature and Sky View Factor are positively correlated a Netherlands$$$ Providing deciduous trees in urban areas and along cycling infrastructures helps improve (Böcker and Thorsson 2014) urban comfort Weather information Singapore$$$ 28.2% of cyclists acquired weather information before the onset of their current trip; this access (Meng et al. 2016) is particularly the case for young adult, male, and employed cyclists Pavement technologies United Kingdom$$$ Reduction by up to 2.5°C in UTCI is found when artificial wetting is applied (Kubilay et al. 2021) United States$$$ Advanced pavement technologies (for example, permeable pavement), green/white (Karner, Hondula, and Vanos 2015) roofs, forced evaporative cooling, and urban agriculture improve comfort Source: Original table for this publication. Note: Shade strategies are common in regions with high heat. UTCI = universal thermal climate index; $$$ = high-income countries; $$ = middle-income countries; $ = low-income countries. a. Sky View Factor (SVF) is a measurement that quantifies the proportion of sky visible from a specific point on the ground. It is expressed as a ratio between 0 and 1. An SVF value of 1 means 100% of the sky is visible (completely open); a value of 0 means no sky is visible (completely obstructed). References Abu Dhabi Urban Planning Council. 2011. Abu Dhabi Public Realm Design Manual. Canadian Institute of Planners. https://www.cip-icu.ca/wp-content/uploads/2023/11/2011-HM-Urban-Design21.pdf Ahmed, F., G. Rose, M. Figliozzi, and C. Jakob. 2012. “Commuter Cyclist’s Sensitivity to Changes in Weather: Insight from Two Cities with Different Climatic Conditions.” Paper prepared for theTransportation Research Board Annual Meeting, Washington, DC, January 2012. Transportation Research Board. https://www.researchgate.net/publication/311220138_Commuter_Cyclist’s_Sensitivity_ to_Changes_in_Weather_Insight_from_Two_Cities_with_Different_Climatic_Conditions Aultman-Hall, L., D. Lane, and R. R. Lambert. 2009. “Assessing Impact of Weather and Season on Pedestrian Traffic Volumes.” Transportation Research Record 2140 (1). https://doi.org/10.3141/2140-04 Böcker, L. and S. Thorsson. 2014. “Integrated Weather Effects on Cycling Shares, Frequencies, and Durations in Rotterdam, the Netherlands.” Weather, Climate, and Society 6 (4): 468–81. https://doi. org/10.1175/WCAS-D-13-00066.1 Bröde, P., E. L. Krüger, F. A. Rossi, and D. Fiala. 2012. “Predicting Urban Outdoor Thermal Comfort by the Universal Thermal Climate Index UTCI: A Case Study in Southern Brazil.” International Journal of Biometeorology 56: 471–80. https://doi.org/10.1007/s00484-011-0452-3 Chàfer, M., C. L. Tan, R. Jacoby Cureau, W. Nuik Hien, A. L. Pisello, and L. F. Cabeza. 2022. “Mobile Measurements of Microclimatic Variables through the Central Area of Singapore: An Analysis from the Pedestrian Perspective.” Sustainable Cities and Society 83: 103986. https://doi.org/10.1016/j. scs.2022.103986 101 Appendix F. Active Transportation Impacts and Mitigation Strategies Helbich, M., L. Böcker, and M. Dijst. 2014. “Geographic Heterogeneity in Cycling under Various Weather Conditions: Evidence from Greater Rotterdam.” Journal of Transport Geography 38: 38–47. https://doi. org/10.1016/j.jtrangeo.2014.05.009 Karner, A., D. Hondula, and J. Vanos. 2015. “Heat Exposure during Non-Motorized Travel: Implications for Transportation Policy under Climate Change.” Journal of Transport & Health 2 (4): 451–59. https://doi. org/10.1016/j.jth.2015.10.001 Kubilay, A., D. Strebel, D. Derome, and J. Carmeliet. 2021. “Mitigation Measures for Urban Heat Island and Their Impact on Pedestrian Thermal Comfort.” Journal of Physics: Conference Series 2069 (1): 012058. IOP Publishing. https://doi.org/10.1088/1742-6596/2069/1/012058 Lewin, A. 2011. “Temporal and Weather Impacts on Bicycle Volumes.” Transportation Research Board. https://trid.trb.org/View/1092520 Meng, M., J. Zhang, Y. Wong, and P. H. Au. 2016. “Effect of Weather Conditions and Weather Forecast on Cycling Travel Behavior in Singapore.” International Journal of Sustainable Transportation 10 (9): 773–80. https://doi.org/10.1080/15568318.2016.1149646 Miranda-Moreno, L. F. and T. Nosal. 2011. Weather or Not to Cycle: Temporal Trends and Impact of Weather on Cycling in an Urban Environment.” Transportation Research Record 2247 (1). https://doi. org/10.3141/2247-06 Mislan, K. A. S., D. S. Wethey, and B. Helmuth. 2009. “When to Worry about the Weather: Role of Tidal Cycle in Determining Patterns of Risk in Intertidal Ecosystems.” Global Change Biology 15 (2): 3056–65. http://dx.doi.org/10.1111/j.1365-2486.2009.01936.x Motoaki, Y. and R. A. Daziano. 2015. “A Hybrid-Choice Latent-Class Model for the Analysis of the Effects of Weather on Cycling Demand.” Transportation Research Part A: Policy and Practice 75: 217–30. https:// doi.org/10.1016/j.tra.2015.03.017 Phung, J. and G. Rose. 2007. “Temporal Variations in Usage of Melbourne’s Bike Paths.” In Proceedings of the 30th Australasian Transport Research Forum edited by J. Morris, 1–15. https://research.monash. edu/en/publications/temporal-variations-in-usage-of-melbournes-bike-paths Queensland Health. 2010. Technical Guidelines for Shade Provision in Public Facilities. Queensland Government. https://www.health.qld.gov.au/__data/assets/pdf_file/0024/443931/tech-guidelines- shade-provision.pdf Sabir, M. 2011. “Weather and Travel Behaviour.” PhD thesis, Vrije Universiteit Amsterdam. https:// research.vu.nl/en/publications/weather-and-travel-behaviour Sun, Q., T. Macleod, A. Both, J. Jurley, A. Butt, and M. Amati. 2021. “A Human-Centred Assessment Framework to Prioritise Heat Mitigation Efforts for Active Travel at City Scale.” Science of the Total Environment 763: 143033. https://doi.org/10.1016/j.scitotenv.2020.143033 Turner, V. K., ., A. Middel, and J. K. Vanos. 2023. “Shade Is an Essential Solution for Hotter Cities.” Nature 619: 694–97. https://doi.org/10.1038/d41586-023-02311-3 Whiting, K. 2023. “Climate Change Is Making Heatwaves More Intense – Here Are 7 Ways the World Can Cope.” Forum Stories, August 4, 2023. World Economic Forum. https://www.weforum.org/ stories/2023/08/climate-change-heatwaves-cooling-solutions/ 102 Appendix F. Active Transportation Impacts and Mitigation Strategies Appendix G User Behavior Impacts and Mitigation Strategies Table G.1  Impacts of Heatwaves on User Behavior and Corresponding Magnitude of Impacts as Identified by Multiple Studies Threshold Impact Country (paper) Method Details / Magnitude of impacts temperatures Mode of travel Global Review n.a. • Leisure travel is more elastic than commuting (Liu, Susilo, and Karlström • Travelers assess the weather conditions prior to 2017) travel India$$ Survey n.a. • 36% of respondents are likely to change mode to (Jain and Singh 2021) access the metro stations • 16% of respondents shift from metro to alternate modes China$$ Toll data and moving 30°C • No significant effect on intercity travel demand (Yang et al. 2021) average model • Significant negative effects freeway traffic • Hot day impacts only real-time travel, not future travel • Effect of weather on weekends more important China$$ Survey and Logit 5°C increment • 27.1% (39.4%) decrease in odds of selecting airplane (Li et al. 2021) model (express bus) over high-speed rail • 18.6% increase in odds of choosing train travel over high-speed rail China$$ Regression 4°C increment • 14.7% increase in market share of cars (Ma et al. 2019) • Cycling is the most affected, compared with walking, public transport, and car travel China$$ GPS trajectories and 1 °C increment • 23% (32%) increase in probability of walking for mild (Otim et al. 2022) Logit model (warm) weather • 21% (17%) decrease in probability of selecting bus for mild (warm) weather Netherlands$$$ Travel diaries and logit Temperature: 24°C • Demand of all modes decrease above threshold (Böcker and Thorsson model MRT: 52 °C temperature 2014) PET: 30°C • Cycling peaks at optimal temperature and a dip in car usage observed Activity Time Greece$$$ Regression n.a. • Stable presence of people in the morning during (Nikolopoulou and summer Lykoudis 2007) • Relatively low numbers after midday hours India$$ Survey n.a. People traveling long distances by metro are unlikely to (Jain and Singh 2021) make any change Algeria$$ Questionnaire and n.a. No medium/long stop carried out in urban areas with (Boumaraf and Amireche video data the sun shining 2020) 103 Heatwaves and Their Effects on Transportation Systems: A Comprehensive Review Threshold Impact Country (paper) Method Details / Magnitude of impacts temperatures Activity Time China$$ Regression model 20°C–25°C Intraday activity substitution: (Fan et al. 2023) • From noon (10 a.m. to 2 p.m.) and late afternoon (3 to 6 p.m.) are changed to morning (6 to 9 a.m.) and evening (7 to 10 p.m.) • A larger substitution occurs when there is greater time flexibility • Switched activities if cooler periods within a day are present • Positives: Reduces heat exposure by 4°C–5°C • Issues: Active time at night delayed by about 30 minutes, potential side effects on sleep quality United States$$$ American Time Use 85 °F Activity decrease for construction labor happens at the (Graff Zivin and Neidell Surveys (ATUS) and end of the day 2014) system of equations Activity Reduction Global Review n.a. Walking and car travel distances are shorter in warmer (Liu, Susilo, and Karlström temperatures 2017) Netherlands$$$ Regression n.a. 80% fluctuation in bicycle flow explained by changes in (Thomas, Jaarsma, & weather Tutert, 2013) Sweden$$$ Regression 30°C Peak-hour traffic less affected by weather (Liu, Susilo, and Karlström 2015) 9 EU Cities$$$ Regression n.a. Diminished positive effect of temperature on walking (de Montigny, Ling, and Zacharias 2012) Greece$$$ Regression n.a. Significant reduction in presence of people in open (Nikolopoulou and spaces Lykoudis, 2007) India$$ Survey n.a. • 16% respondents decided to cancel their trip (Jain and Singh 2021) • People using two-wheelers to access the metro are more likely to cancel their trip China$$ Regression model 20°C–25°C • 5% less outdoor leisure activity with temperatures > (Fan et al. 2023) 30°C; 13% less with temperatures > 35°C. • Inverted U curve observed for park visits with hourly temperature, but not for daily temperature. • Reduction in physical activity: By 2100, 5.7% reduction in July (hottest) and 4.7% increase in February (coldest) in China United States$$$ American Time Use 85°F • 1 hour reduction in daily work time for workers in (Graff Zivin and Neidell Surveys (ATUS) and industries 2014) System of equations • Demand factors limit workers’ discretion • Inverted U curve observed for outdoor leisure • 22 minutes reduction in outdoor leisure for temperatures > 100°F compared to 76°F–80°F • Reduction is most pronounced for unemployed people United States$$$ Citi Bike bikeshare 28.1°C Total hours’ bike rider decrease above threshold in New (Heaney et al. 2019) data and Generalized York Additive Models Activity Reduction China$$ Toll data and moving 30°C • No significant effect on intercity travel demand (Yang et al. 2021) average model • Significant negative effects on freeway traffic • Hot day impacts only real-time travel, not future travel • Effect of weather on weekends is more important 104 Appendix G. User Behavior Impacts and Mitigation Strategies Threshold Impact Country (paper) Method Details / Magnitude of impacts temperatures Trip Perception Netherlands$$$ Structural Equation 25°C • Too hot weather negatively affects en-route place (Böcker et al. 2015) model valuations • Aesthetics, friendliness, and liveliness turn negative with weather that is too hot Algeria$$ Questionnaire and n.a. • Positive outlook of high temperatures for people (Boumaraf and Amireche Video data who visit frequently and know the location well 2020) • “Visual construct” primarily depends on perception of pleasant weather Qatar$$$ Survey 25.6°C PET: Warm • 46% of participants prefer a cooler environment in (Alattar and Indraganti season the warm season 2023) 22.3°C PET: Cool • 38% of participants indicate a preference for season stronger winds during warm season (38%) • 39% would have liked less sun Source: Original table for this publication. Note: These include changes in mode of travel, activity time, activity reduction, and trip perception. n.a.-= not available; MRT = mean radiant temperature; PET = physiologically equivalent temperature; $$$ = high-income countries; $$ = middle-income countries; $ = low-income countries. Table G.2  Various Adaptation Strategies for Changes in User Behaviors Strategy Country (paper) Details / Strategy effectiveness Physical acclimation China$$ Acclimation not observed even for people more frequently exposed to hot (Fan et al. 2023) temperatures United States$$$ Temporal substitutions as well as physical acclimatization are important (Graff Zivin and Neidell 2014) Qatar$$$ • Higher (25.6°C) neutral PET observed for warm season while lower (22.3°C) (Alattar and Indraganti 2023) for cool season • People tolerate higher temperatures in the warm season India$$ 29°C–35°C: Observed neutral temperature significantly higher than standard (Deevi and Chundeli 2020) neutral temperature (18°C–23°C) Psychological / China$$ Habits of avoiding the hottest period of day are more well-developed behavioral (Fan et al. 2023) adaptation United States$$$ Protective behavior is an important channel for minimizing potential health (Graff Zivin and Neidell 2014) impacts Qatar$$$ • Shift to better sensation with 5°C PET in warm season and with 6.8°C PET (Alattar and Indraganti 2023) in cold season • More sensitive thermal sensation during warm season • People are able to accept their surrounding environment and adapt to a wide range of thermal conditions in the long term. • People’s thermal sensations are greatly affected by the reason for their travel Greece$$$ In summer, visitors prefer to sit in shaded areas (Nikolopoulou and Lykoudis 2007) Source: Original table for this publication. Note: Both physical and psychological adaptation have been discussed in the literature. PET = physiologically equivalent temperature; $$$ = high-income countries; $$ = middle-income countries; $ = low-income countries. 105 Appendix G. User Behavior Impacts and Mitigation Strategies References Alattar, D. and M. Indraganti. 2023. “Investigation of Outdoor Thermal Comfort and Psychological Adaptation in Hot-Humid Climate of Qatar.” E3S Web of Conferences 396: 05015. https://www.e3s- conferences.org/articles/e3sconf/abs/2023/33/e3sconf_iaqvec2023_05015/e3sconf_iaqvec2023_05015. html Boumaraf, H. and L. Amireche. 2020. “The Impact of Microclimates on the Variation of User Density and the Length of Time Users Stay in Areas of Public Space in Arid Regions.” Intelligent Buildings International. 12 (2): 133–49.  https://doi.org/10.1080/17508975.2018.1522498 Böcker, L., M. Dijst, J. Faber, and M. 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