What drives urban transportation safety? Exploring the role of modal composition and travel exposure

Abstract

Past urban transportation safety efforts have largely focused on controlling road user behavior through tactics such as speed management and separating users in space and time. This research moves beyond roadway behavior to examine associations between kinetic energy exposure and safety via travel behavior factors such as vehicle miles traveled (VMT) and mode share. After analyzing 227 USA urban areas and controlling for state-level heterogeneity via linear mixed-effects models, we found that kinetic energy exposure is more strongly associated with transportation safety outcomes than variables focused on roadway behavior such as vehicle speeds, education requirements, enforcement efforts, alcohol involvement or seat belt use. Urban areas with lower commute mode share by car and, to a lesser extent, lower VMT are most strongly associated with lower per capita transportation fatality rates. These results add new knowledge by suggesting that, in addition to focusing on trying to get people to behave better on the roads – as many current safety frameworks do – reducing driving exposure by facilitating shorter driving distances and providing viable multimodal options is also strongly associated with improved safety outcomes. The findings suggest that prevailing transportation safety paradigms, such as the Safe System Approach, may benefit from greater consideration of driving exposure.