A Framework for Assessing Cumulative Exposure to Extreme Temperatures During Transit Trip

The combined influence of urban heat islands, climate change, and extreme temperature events are increasingly impacting transit travelers, especially vulnerable populations such as older adults, people with disabilities, and those with chronic diseases. Previous studies have generally attempted to address this issue at either the micro- or macro-level, but each approach presents different limitations in modeling the impacts on transit trips. Other research proposes a meso-level approach to address some of these gaps, but the use of additive exposure calculation and spatial shortest path routing poses constraints meso-modeling accuracy. This study introduces HeatPath Analyzer, a framework to assess the exposure of transit riders to extreme temperatures, using TransitSim 4.0 to generate second-by-second spatio-temporal trip trajectories, the traveler activity profiles, and thermal comfort levels along the entire journey. The approach uses heat stress combines the standards proposed by the NWS and CDC to estimate cumulative exposure for transit riders, with specific parameters tailored to the elderly and people with disabilities. The framework assesses the influence of extreme heat and winter chill. A case study in Atlanta, GA, reveals that 10.2% of trips on an average summer weekday in 2019 were at risk of extreme heat. The results uncover exposure disparities across different transit trip mode segments, and across mitigation-based and adaptation-based strategies. While the mitigation-based strategy highlights high-exposure segments such as long ingress and egress, adaptation should be prioritized toward the middle or second half of the trip when a traveler is waiting for transit or transferring between routes. A comparison between the traditional additive approach and the dynamic approach presented also shows significant disparities, which, if overlooked, can mislead policy decisions.