Study Details

Study Title: Assessing Effects of Transit Signal Priority on Traffic Safety: Empirical Bayes Before-After Study Using King County, Washington Data

Authors: Song and Noyce

Publication Date: JAN, 2018

Abstract: Transit signal priority (TSP) has become popular among cities in the United States as a transit preferential treatment that improves transit operational performance through adjusting signal timing when transit vehicles are approaching signalized intersections. The majority of attention has been given to the operational effects of TSP. Few prior studies have discussed such a system’s effects on traffic safety, with even fewer studies investigating North American implementations. Prior assessment results were mixed, leaving the understanding of TSP’s safety effects remain unclear. The purpose of this study is to add to the existing research on this topic, and to get a better understanding of TSP’s safety effects. An Empirical Bayes (EB) before-after analysis was carried out using TSP implementation data from King County, Washington. Eleven transit corridors having TSP activated in 2010-2014 were assessed, and 75 street sections without TSP treatment were selected to form a reference group. The EB analysis results showed a 13% reduction in total crashes with the implementation of TSP, a 16% reduction in property-damage-only crashes, and a 5% reduction in fatal and injury crashes. These results are consistent with most existing TSP safety studies. The study implies TSP brings road safety benefits to transit corridors in a U.S. metropolitan setting, and suggests transportation and transit agencies to add safety assessment into future TSP practices.

Study Citation: Song, Y., and D. Noyce. "Assessing Effects of Transit Signal Priority on Traffic Safety: Empirical Bayes Before-After Study Using King County, Washington Data". Presented at the 97th Annual Meeting of the Transportation Research Board, Paper No. 18-03340, Washington, D.C., (2018).


CMFs Associated With This Study

Category: Transit

Countermeasure: Implement transit signal priority

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.873 12.7 4 Stars All All Not specified Urban
0.841 15.9 4 Stars All O Not specified Urban
0.949 5.1 3 Stars All K,A,B,C Not specified Urban