  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.
