METHODOLOGY

Safety effects of RLCs were evaluated through a before and after study and equivalent property damage only (EPDO) analysis. Crash data such as severity, type, and signal status were collected and examined across eight intersections, four intersections were equipped with RLCs and four intersections without RLCs. Total crashes and red light running were seen to decrease, but rear end crashes increased which was consistent with expectations. Therefore, to standardize improvement measurement, each crash was multiplied by its EPDO factor which determines severity. EPDO factors are taken from NHTSA 2015 crash cost estimates. A reduction in total EPDO score indicates an improvement in safety.

FINDINGS

• The results indicated that presence of RLCs at intersections can influence driver behavior including higher tendencies to stop at the intersections leading to longer intersection delays.
• Although the methodology does not account for regression to the mean bias or traffic volume, the overall EPDO score showed an improvement of 22 percent after using RLCs. Due to the small samples, it may overweight intersections with a small number of crashes, and a statistical significance test was not performed. However, the generally positive trend in the results hints at some level of improvement. The table below presents the measured scores at each experimented intersection.

Table 1. EPDO scores at the four treatment sites (using NHTSA 2015 Weights