Measuring Exposure to Extreme Heat in Public Transit Systems

Abstract

Public transit users are among the most vulnerable to extreme heat due to urban heat island effect and longer outdoor exposure. However, few studies have investigated transit riders’ heat exposure and considered exposure time and travel behavior when calculating heat exposure. This paper introduces a holistic measurement system – Transit Heat Exposure Index (THEI) – to gauge high-fidelity heat exposure for transit riders and apply the method to Miami, one of the hottest US cities. By using high-resolution meteorological and built environment data, we calculate 1m-by-1m feels-like temperature for Miami-Dade Transit with microclimate simulation techniques. Then, we calculate the detailed travel time between all census block groups in Miami with realistic transit routing technique. We then adopt a total time-degree approach to calculate heat exposure and aggregate THEI at different levels. Our results show that despite higher local feels-like temperature, downtown Miami has lower heat exposure due to better transit access. Source analysis also shows that walking is the primary source of heat compared to waiting, and a small portion of streets and bus stops contribute most heat exposure. This method provides first-hand evidence for future heat planning, enabling more effective strategies to mitigate extreme heat's impact on transit riders.

Keywords: Heat Exposure, Public Transit, Urban heat island effect, microclimate simulation, Thermal comfort, Transit Heat Exposure Index