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Abstract

Despite bicycling being considered on the order of ten times more dangerous than driving, the evidence continues to build that high-bicycling-mode-share cities are not only safer for bicyclists but for all road users. This paper looks 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 differences in the physical places or the people that inhabit them? Based on thirteen years of data from twelve large U.S. cities, we investigated over 17,000 fatalities and more than 77,000 severe injuries across nearly 8,700 block groups via multilevel, longitudinal, negative binomial regression models. We hypothesize three potential 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 and socio-economic differences (e.g. as some cities may be more populated by those with lower transportation injury risks).

The results suggest that more bicyclists on the road is not the underlying 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 even more strongly so, across the city as a whole. Higher intersection density, which typically corresponds to a more compact and lower-speed built environment, 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 first chapter helps support an evidence-based approach to building safer cities for all road users. 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 the potential pathways toward safer cites are complementary and should not be considered in isolation. Moreover, our results – particularly the safety disparities associated with gentrification – suggest equity issues and the need for future research.

How to Cite

Marshall, Wesley E., Nick Ferenchak, and Bruce Janson. Why Are Bike-Friendly Cities Safer for All Road Users?, MPC-18-351. North Dakota State University - Upper Great Plains Transportation Institute, Fargo: Mountain-Plains Consortium, 2018.