Safety Evaluation of Flashing Yellow Arrows for Protected/Permissive Left-Turn Control

In the spring of 2010, the Illinois Department of Transportation initiated an areawide implementation of the flashing yellow arrow (FYA) as the display for the left-turn permissive interval at more than 100 intersections operating with protected/permissive left-turn (PPLT) control in the Peoria, Illinois, area. Bradley University researchers evaluated the effectiveness of FYAs on safety at 86 intersections and 164 approaches where no other improvements were made. The effectiveness evaluation was performed using three years of “before FYA installation” crash data and three years of “after FYA installation” crash data using the naïve before and after and empirical Bayes methods for highway safety evaluation. In the “before” condition, the left-turn signals operated with a circular green ball for the permissive interval of PPLT control and a fivesection signal head, while in the “after” condition, the FYA was displayed for the permissive interval of PPLT with a four-section signal head. Supplemental traffic signs with text “Left Turn Yield on Flashing Yellow Arrow” were mounted on the mast arm adjacent to the left-turn signal at over half of the FYA installations. This report presents the results of the comprehensive safety evaluation of FYA for PPLT control, focusing on the targeted crash types of left-turn-related crashes, and specifically, left-turn opposing through crashes. Analyses were also performed to assess the effects of the FYA supplemental signs and to assess the effects of the FYA overall on two subsets of drivers: older drivers (age 65+) and younger drivers (age 16 to 21 years). Crash modification factors for statistically significant crash reductions at the FYA approaches based on the empirical Bayes method are provided. The findings of this research, conducted on 164 FYA approaches in the Peoria area indicate that FYAs for PPLT control improve safety for left-turning vehicles. The results of the economic effectiveness of the FYAs yielded a benefit to cost ratio of 19.8 to 1.0. The results of this research may be used to make informed decisions on future installations of the FYA countermeasure to improve safety at signalized intersections.Illinois Department of Transportation, R27-097Ope