Advancing healthy cities through safer cycling: An examination of shared lane markings

Abstract

To advance healthy transportation via increased bicycling, cities combat one of the primary barriers to such cycling – traffic safety concerns – through the provision of various bicycle treatments. Shared lane markings (more commonly known as “sharrows”) are an increasingly common treatment utilized to improve bicyclist safety. While past research confirms that sharrows may effectively influence spacing and other operational measures, the impact on actual safety outcomes remains unsubstantiated due to a lack of dooring-related bicycle crash data. Fortunately, the city of Chicago instituted a program to collect dooring crash data in 2010. Thus, the purpose of this research is to longitudinally examine the association between sharrows and bicyclist injuries by combining traditional crash data with dooring-related crash data.To perform this examination, we divide Census block groups in Chicago into three categories based on what bicycle treatment was installed between the years 2011 and 2014: (i) those block groups with no bicycle facilities installed; (ii) those with only sharrows installed; or (iii) those with only bicycle lanes (standard, buffered, and/or protected) installed. Negative binomial regressions and Kruskal–Wallis tests suggest that block groups with only sharrows installed experienced the largest increase in bicyclist injury rates, with exposure being accounted for through levels of bicycle commuter activity. This relationship held true for overall crashes as well as for dooring-related crashes. These findings raise concerns regarding the safety effectiveness of sharrows as used by the City of Chicago during the study period and should be a call for more research on the subject in a variety of different contexts using various exposure metrics. Keywords: Shared lane markings, Sharrows, Bicycle lane, Safety, Dooring crashes