Heat exposure during non-motorized travel: Implications for transportation policy under climate change

Transportation planning agencies around the world are increasingly seeking to develop transportation systems that encourage walking, bicycling, and transit use in order to simultaneously achieve public health and environmental sustainability goals. Under future scenarios that will see increasing global mean temperatures, trips that entail physical exertion outdoors are likely to account for substantial portions of some individuals' overall exposure to potentially dangerous air temperatures. This exposure pathway is poorly understood. In this study we develop a new method to assess outdoor heat exposure during non-motorized travel by combining simulated urban meteorology and transportation-activity data. We demonstrate its utility through application to several real-world planning issues using data from the San Francisco Bay Area. Specifically, we examine spatial and social disparities in heat exposure and find that socially disadvantaged (low-income people and zero-vehicle households) groups are disproportionately exposed to transport-related heat. Since the propensity to walk and bicycle tends to decrease with socioeconomic status (SES) and because lower SES groups are more vulnerable to heat-related health impacts, efforts to mitigate heat exposure can be of disproportionate benefit to these groups. Finally, we demonstrate how the results can be used to supplement more traditional indicators of heat vulnerability that to date do not directly account for actual length of outdoor exposure. The methodology developed here has the potential to guide healthy, sustainable, and equitable urban planning efforts.