“Complete Streets” and Adult Bicyclist Fatalities: Applying G-Computation to Evaluate an Intervention That Affects the Size of a Population at Risk

Abstract “Complete streets” policies require transportation engineers to make provisions for pedestrians, bicyclists, and mass transit users. These policies may make bicycling safer for individual cyclists while increasing the overall number of bicycle fatalities if more people cycle due to improved...

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Bibliographic Details
Published in:American journal of epidemiology 2018-09, Vol.187 (9), p.2038-2045
Main Authors: Mooney, Stephen J, Magee, Caroline, Dang, Kolena, Leonard, Julie C, Yang, Jingzhen, Rivara, Frederick P, Ebel, Beth E, Rowhani-Rahbar, Ali, Quistberg, D Alex
Format: Article
Language:English
Subjects:
Bicycles
Bicycling
Commuting
Computation
Confidence intervals
Estimates
Fatalities
Mortality
Pedestrians
Policies
Population
Practice of Epidemiology
Public transportation
Streets
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Summary:Abstract “Complete streets” policies require transportation engineers to make provisions for pedestrians, bicyclists, and mass transit users. These policies may make bicycling safer for individual cyclists while increasing the overall number of bicycle fatalities if more people cycle due to improved infrastructure. We merged county-level records of complete streets policies with Fatality Analysis Reporting System counts of cyclist fatalities occurring between January 2000 and December 2015. Because comprehensive county-level estimates of numbers of cyclists were not available, we used bicycle commuter estimates from the American Community Survey and the US Census as a proxy for the cycling population and limited analysis to 183 counties (accounting for over half of the US population) for which cycle commuting estimates were consistently nonzero. We used G-computation to estimate the effect of complete streets policies on overall numbers of cyclist fatalities while also accounting for potential policy effects on the size of the cycling population. Over a period of 16 years, 5,254 cyclists died in these counties, representing 34 fatalities per 100,000 cyclist-years. We estimated that complete streets policies made cycling safer, averting 0.6 fatalities per 100,000 cyclist-years (95% confidence interval: −1.0, −0.3) by encouraging a 2.4% increase in cycling but producing only a 0.7% increase in cyclist fatalities. G-computation is a useful tool for understanding the impact of policy on risk and exposure.
ISSN:0002-9262
1476-6256
DOI:10.1093/aje/kwy100