Bicyclist Crash Comparison of Mixing Zone and Fully Split Phase Signal Treatments at Intersections with Protected Bicycle Lanes in New York City

Abstract

This study builds on the success of New York City’s protected bicycle lanes (PBLs) through improving the understanding and impacts of different intersection designs. Specifically, to understand better the safety of the two primary intersection design treatments for single direction PBLs, the mixing zone and fully split phase signal, several different data sources are used in a before–after and cross-sectional analysis including; 184 intersections, nearly 17 years of reported bicycle injury crashes at intersections, and historic bicycle volume and turning movement counts. It was found that, following the installation of PBLs, the rate of crashes per bicyclist decreased by an average of 30%. The study also identified similar benefits between mixing zones and fully split phases at intersections with lower turn volumes while at higher turn volume locations the shorter mixing zones have the lowest crash rates. For wider cross-streets, the crash risk for bicycle riders increased regardless of the treatment, however fully split phase intersections perform better at wider crossings overall. Based on these results, it is recommended that the fully split phase treatment should be typically prioritized where the safety need is greatest, such as at wider intersections and two-way cross-streets. In addition, these findings reinforce the need to reduce turn speeds and cyclist exposure at multilane crossings.