Safety Effect of Different Left-Turn Signal Phasing in Opposing Directions

Very few, if any, studies have investigated safety effects when different left-turn phasing is used on opposing approaches to a signalized intersection. This study considers two groups of northern Virginia signal approaches: a subject group, containing locations with protected/permissive left-turn (PPLT) phasing on one approach and protected-only left-turn (PLT) phasing on the opposing approach and a control group, containing locations with PPLT phasing on both opposing approaches. The study focuses on 18 intersection opposing approaches in the subject group and 505 opposing approaches in the control group, and compares crash patterns for the two groups using crash data from 2003 through 2007. A crash rate analysis shows that the subject group shows an average crash rate higher than the control group. The crash prediction model, for a given AADT, number of opposing lanes and speed limits, confirms similar results, more permissive left-turn crashes when left-turn signal phasing is different on opposing approaches. Due to the limited number of intersections evaluated, further studies are recommended to validate the results.