Why cities with high bicycling rates are safer for all road users.

Despite bicycling being considered ten times more dangerous than driving, the evidence suggests that high-bicycling-mode-share cities are not only safer for bicyclists but for all road users. The authors look to understand what makes these cities safer. Are the safety differences related to ‘safety-in-numbers’ of bicyclists, or can they be better explained by built environment differences or the people that inhabit them? Based on thirteen years of data from twelve large U.S. cities, the authors investigated over 17,000 fatalities and 77,000 severe injuries across nearly 8700 block groups via multilevel, longitudinal, negative binomial regression models. They hypothesize three pathways towards better road safety outcomes: i) travel behavior differences (e.g. ‘safety-in-numbers’ or shifts to ‘safer’ modes); ii) built environment differences (e.g. infrastructure that helps promote safer environments); and iii) socio-demographic/ socio-economic differences (e.g. some cities may be populated by those with lower road safety risk). The results suggest that more bicyclists is not the reason these cities are safer for all road users. Better safety outcomes are instead associated with a greater prevalence of bike facilities – particularly protected and separated bike facilities – at the block group level and, more strongly so, across the overall city. Higher intersection density, which typically corresponds to more compact and lower-speed built environments, was strongly associated with better road safety outcomes for all road users. The variables representing gentrification also accounted for much of our explainable variation in safety outcomes. This paper provides an evidence-based approach to building safer cities. While the policy implications of this work point to protected and separated bike infrastructure as part of the solution, we need to keep in mind that these approaches are complementary and should not be considered in isolation. Moreover, these results – particularly the safety disparities associated with gentrification – suggest equity issues and the need for future research. (Author/publisher)