A new study from researchers at Arizona State University, the University of Washington, and the University of Texas at Austin reveals that extreme heat profoundly affects daily life and travel patterns.
The study, published in Transportation Research Part D: Transport and Environment, found that people change how they go about their days in response to high temperatures, with significant reductions in outdoor activities and shifts in transportation preferences. As cities worldwide face rising temperatures, the study highlights the need for urgent policy interventions.
Led by Ram M. Pendyala, a professor at Arizona State University, along with co-authors Irfan Batur, Victor O. Alhassan, Mikhail V. Chester, and Steven E. Polzin from ASU; Cynthia Chen from the University of Washington; and Chandra R. Bhat from the University of Texas at Austin, the research analyzed how extreme heat alters activity, mobility, and time use patterns.
Using data from the American Time Use Survey (ATUS) and weather data from the National Oceanic and Atmospheric Administration (NOAA), the study focused on 11 major U.S. metropolitan areas, including New York, Los Angeles, and Phoenix.
The collaborative study was supported by two major research initiatives: a National Science Foundation (NSF) LEAP-HI project led by the University of Washington and U.S. Department of Transportation University Transportation Centers (UTCs) led by ASU (TOMNET) and the University of Texas at Austin (TBD).
The research revealed that extreme heat alters people’s routines, particularly when temperatures exceed tolerable limits. On extremely hot days, individuals tend to stay indoors, reduce non-essential travel, and avoid outdoor activities like shopping, socializing, and recreation. Many shift their travel schedules, opting for early morning or late evening outings to avoid the midday heat.
Transportation choices also change dramatically under extreme heat conditions. Car use rises, while the use of public transit, walking, and biking decreases significantly. The study found that public transit trips fall by nearly 50% on extreme heat days as people turn to air-conditioned private vehicles. This shift presents a challenge for cities aiming to promote sustainable transportation options in the face of climate change.
“We need to understand how extreme heat impacts transportation behavior if we want to build more resilient and sustainable cities,” said Pendyala. “This study offers critical insights into the ways climate change could reshape urban mobility.”
The study also uncovered disparities in how different socio-demographic groups respond to extreme heat. Low-income individuals and those without access to cars are more reliant on walking or public transportation, leaving them more vulnerable to dangerous temperatures. Unlike higher-income individuals, who report reducing trips on hot days, low-income populations do not show significant drops in travel, even in extreme conditions.
This lack of flexibility puts disadvantaged groups at greater risk of heat-related health issues, according to the researchers.
“We see that extreme heat exacerbates inequities in mobility and activity-travel participation,” Pendyala explained. “Those who are already at a disadvantage face even greater risks during heatwaves. This is a clear call for targeted policy interventions to protect the most vulnerable population groups.”
Older adults also face challenges in adapting to extreme heat, with the study finding that seniors are more likely to experience social isolation when they shelter indoors to avoid high temperatures.
To address the findings, the authors propose several policy recommendations aimed at protecting communities from extreme heat. These include creating shaded public spaces, offering on-demand transportation for vulnerable populations, and declaring “heat days” during extreme weather when travel and work are minimized. Much like snow days, these heat days would allow people to stay home and access cooling centers if needed.
Urban design also plays a role in heat mitigation, with strategies like planting trees and using reflective materials on streets and sidewalks to reduce the urban heat island effect.
According to co-author Irfan Batur: “Addressing the challenges associated with extreme heat is not just a matter of urban design, but of equity and public health and wellbeing.”
The research points to the importance of incorporating heat mitigation into transportation and urban planning. As extreme heat becomes more frequent and intense with climate change, cities face growing pressure to reduce residents’ exposure and strengthen protection against heat-related risks.
The study’s findings offer a critical message for policymakers.
“This research sheds light on how heat can disrupt daily life and travel in ways that are potentially harmful for the most vulnerable population groups,” Pendyala noted. The team hopes that their work will spur meaningful change, pushing cities to create environments where residents can stay safe, active, and mobile despite rising temperatures.
Journal Reference:
Irfan Batur, Ram M. Pendyala, Chandra R. Bhat, Cynthia Chen, Victor O. Alhassan, Mikhail V. Chester, and Steven E. Polzin, ‘Understanding how extreme heat impacts human activity-mobility and time use patterns’, Transportation Research Part D: Transport and Environment 136, 104431 (2024). DOI: 10.1016/j.trd.2024.104431
Article Source:
Press Release/Material by Arizona State University (ASU)
Featured image credit: yanalya | Freepik
