Study Details

Study Title: Investigating Effect of Collision Aggregation on Safety Evaluations Using Multivariate Linear Intervention Models: Case Study of Signal Head Upgrade Program

Authors: El-Basyouny et al.

Publication Date: JAN, 2012

Abstract: This paper investigates the effect of collision aggregation on safety evaluation using a case study from the Insurance Corporation of British Columbia (ICBC) 2001 Signal Head Upgrade Program. Three different types of evaluations were carried out. Bivariate intervention models were used in the first two evaluations to assess the safety impact of different collision severity levels (severe and property-damage-only) and the impact of the time of the collision(day-time and night-time). In the third evaluation, multivariate intervention models were utilized to determine the safety impacts of the program on each combination of collision severity and time of occurrence (i.e. severe/day-time, severe/night-time, PDO/day-time, PDO/night-time). Overall, the results indicated the effectiveness of the program in improving the safety of the treated intersections. However, the results reveal that aggregate analyses can lead to misleading results. Aggregating collisions over time of day indicated the treatment had significant reductions on PDO collisions but not severe collisions. Alternatively, aggregating collisions over severity levels indicated the treatment had significant reductions on both day- and night-time collisions. These results are different from the results of the disaggregate analysis, where significant reductions were found for all collision types except for day-time severe collisions.

Study Citation: El-Basyouny, K.; Sayed, T.; El Esawey, M; and Pump, J. E. "Investigating the Effect of Collision Aggregation on Safety Evaluations using Multivariate Linear Intervention Models: Case Study of Signal Head Upgrade Program." Presented at the Transportation Research Board 91st Annual Meeting, Paper No. 12-2093, January 22-26, 2012, Washington, DC.

Study Report: Download the Study Report Document


CMFs Associated With This Study

Category: Intersection traffic control

Countermeasure: Improve signal visibility, including signal lens size upgrade, installation of new back-plates, addition of reflective tapes to existing back-plates, and installation of additional signal heads

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.004 -0.4 4 Stars Day time K,A,B,C Not Specified Urban
0.902 9.8 5 Stars Nighttime K,A,B,C Not Specified Urban
0.901 9.9 5 Stars Day time O Not Specified Urban
0.867 13.3 5 Stars Nighttime O Not Specified Urban