Evaluating impact on safety of improved signal visibility at urban signalized intersections

Abstract

A study evaluated the safety impacts associated with improved signal visibility at urban signalized intersections. The improvements included one or a combination of the following upgrades: signal lens size, new backboards, reflective tapes added to existing backboards, and additional signal heads. Intersection collision data based on insurance claim records from the Insurance Corporation of British Columbia were used in the study to evaluate the effectiveness of the signal visibility improvement These automobile insurance claim data are current, comprehensive, and considered quite reliable for intersection locations. Traffic volume and collision data were collected for treatment and comparison groups. The treatment group included 139 intersections and the comparison group included 85 intersections. The data for the comparison group were used to account for history and maturation confounding factors. An empirical Bayes analysis was used to ensure that the evaluation results were reliable and to account for the regression-to-the-mean confounding factor. The analysis was undertaken for both severe (injury + fatal) and property-damageonly (PDO) collisions and also for daytime and nighttime collisions. The evaluation results indicate statistically significant reductions of 8.5%, 5.9%, 6.6%, and 7.3% for PDO, daytime, nighttime, and total collisions, respectively. Severe collisions showed a nonsignificant reduction of 2.6 %.