The cost of climate change: A generalized cost function approach for incorporating extreme weather exposure into public transit accessibility

Public transit offers urban populations physical accessibility to resources and opportunities. However, at the same time, transit trips often expose users to extreme environmental conditions, such as extreme heat and cold since transit journeys usually include out-of-vehicle trip segments including walking and waiting. Such exposure can be considered as environmental health costs because exposure to weather extremes can lead to adverse health outcomes. Even worse, climate change is increasing the intensity and frequency of extreme weather events. In this context, how can we make public transit accessibility measures ready for climate change? This paper attempts to answer this question by developing a generalized cost function approach combining travel time and environmental health costs into an integrated measure of dual accessibility: a measure of the travel costs of accessing a fixed number of destinations. We synthesize transport science, environmental health, remote sensing, and urban climatology to empower the proposed framework. To demonstrate the utility of the proposed method, we carry out an example study that incorporates transit passengers' extreme cold exposure into accessibility measures in the city of Winnipeg, Manitoba, Canada. Further, we perform a social equity analysis to investigate whether the increase in total integrated costs (i.e., decrease in accessibility) due to the inclusion of environmental health costs disproportionately affects socially disadvantaged population groups. The proposed method enables a more realistic and practical measurement of public transit accessibility under climate change; thereby, improving the readiness and resilience of our society and transport systems for future challenges.