The Intersection of Extreme Heat, Public Transit, and Social Vulnerability: A Systematic Review

Background and Purpose: Extreme heat presents a significant health threat in the United States. While extreme heat affects individuals from all socioeconomic backgrounds, those reliant on public transit face disproportionate risk due to heat exposure while traveling, which could potentially impact riders’ health. Moreover, individuals who rely on public transit often have the lowest median income and are less likely to own a personal vehicle. Therefore, social vulnerability— the susceptibility of social groups to the adverse impacts of natural hazards—plays a crucial role when assessing heat impacts. The intersection of heat-related health risks with public transit and social vulnerability has not yet been comprehensively studied. This study systematically reviewed peer-reviewed literature aiming to address this knowledge gap.

Methods: Using the PRISMA guideline, searches were conducted in four databases: SCOPUS, Web of Science, PubMed, and APA PsycINFO for English-language articles published between 1990 and the present. Search terms were: Title/Abstract (thermal OR heat OR “heat wave” OR “extreme heat” OR “urban heat” OR “Urban Heat Island” OR UHI OR “climate change”) AND ABS (“public transportation” OR “public transit” OR “public transport” OR bus OR rider OR passenger) AND ABS (marginalized OR vulnerability OR vulnerable OR health OR mortality OR fatality OR effect OR impact OR symptom OR illness OR disorder OR risk OR hazard OR hospitalization).

Results: The search strategy identified 634 initial articles, eventually reduced to a final sample of 15. Seven themes were identified: (i) the intersection of weather, public transit, and social vulnerability; (ii) riders’ thermal comfort in a bus and bus stops; (iii) consequences of heat exposure on bus drivers; (ⅳ) riders’ and bus drivers’ coping behaviors to responding to heat; (ⅴ) travel experiences regarding weather conditions; (ⅵ) effect of mist spray system in bus stops; and (ⅶ) thermal conditions of metro stations. Most researchers studied bus stop infrastructure and thermal conditions, with two examining riders’ and bus drivers’ responses to heat and five exploring the intersection of public transit infrastructure and social vulnerability.

Conclusions and Implications: This study synthesized the literature to explore the intersection of extreme heat, public transit, and social vulnerability. However, no research has been found to comprehensively identify the intersection of riders’ experiences using public transit, their social vulnerability, and heat-related health risks. The implications are as follows: (i) considering demographic factors and regional differences: future studies examining riders’ heat-related health risks may need to consider demographic factors such as income, education, race, age, gender, disability, health status, and the characteristics of cities or geographic areas; (ii) diversification of research methods and data collection: it will help to enhance the understanding of riders’ lived experiences and identify the actual impact of heat while riding a bus; (iii) embedding results to policy and practice: it may need to examine how findings from studies can be incorporated into policies and practices to strengthen community resilience to heat; and (ⅵ) collaboration: addressing the impact of heat on riders’ health necessitates interdisciplinary work among experts such as climate scientists, urban planners, health personnel, and citizens.