Hot and bothered: Exploring the effect of heat on pedestrian route choice behavior and accessibility

Although many cities are incentivizing non-auto modes of transportation in response to the climate crisis, their sustainable mobility transition efforts are being challenged by the rising intensity and frequency of heatwaves. Pedestrians are exposed to high levels of heat stress on hot days, which may reduce their willingness to walk. It is thus important to understand how heat affects pedestrian behavior and accessibility, so that climate mitigation strategies can be better targeted to support walking as a mode of transport but also as a first-/last-mile connection to public transit. In this study, we used a dataset of pedestrian trips undertaken during the summer of 2014 in Boston, MA. Along with several route attributes (such as length, turns, sidewalk width, amenities, Normalized Difference Vegetation Index, and Sky View Factor), we also included a measure of heat stress (Universal Thermal Climate Index - UTCI) to explain pedestrian route choice behavior. Using path-size logistic regression models, we found evidence to suggest that heat stress has a considerable and statistically significant effect on the perceived walking distance. We also found that the effect was non-uniform and possibly exponential. Additionally, we illustrated the extent to which heat stress can reduce pedestrian accessibility to important destinations (such as public transit). This reduction was significant on a typical summer day, with an even sharper reduction on the hottest summer day. Non-White residents were observed to have lower accessibility levels compared to all pedestrians, likely because of disparities in urban heat exposure. Our findings highlight the importance of incorporating heat exposure into transportation planning and urban design frameworks, especially with an equity lens to address unequal consequences.