Study Details

Study Title: Evaluating the Safety Impacts of Improving Signal Visibility at Urban Signalized Intersections

Authors: Sayed et al.

Publication Date: 2007

Abstract: This paper describes a study that was undertaken to evaluate the safety impacts that are associated with improved signal visibility at urban signalized intersections. The improvements included one or a combination of the following upgrades: signal lens size upgrade, installing new backboards, adding reflective tapes to existing backboards, and installing 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. This auto insurance claims 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 are reliable and to account for the regression to the mean confounding factor. The analysis was undertaken for both severe (injury + fatal) and property damage only (PDO) collisions and also for day-time and night-time collisions. The evaluation results indicate statistically significant reductions of 8.5%, 5.9%, 6.6% and 7.3% for PDO, day-time, night-time, and total collisions, respectively. Severe collisions showed a non-significant reduction of 2.6%.

Study Citation: Sayed, T., El Esawey, M., and Pump, J., "Evaluating the Safety Impacts of Improving Signal Visibility at Urban Signalized Intersections." 2007 TRB 86th Annual Meeting: Compendium of Papers CD-ROM, Vol. TRB#07-135, Washington, D.C., (2007)

CMFs Associated With This Study

Category: Intersection traffic control

Countermeasure: Improve visibility of signal heads

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.93 7 4 Stars All All Not specified Urban
0.97 3 4 Stars All K,A,B,C Not specified Urban
0.91 9 4 Stars All O Not specified Urban
0.94 6 4 Stars All All Not specified Urban
0.93 7 4 Stars Nighttime All Not specified Urban