RELATIONSHIPS BETWEEN TRAFFIC OPERATIONS AND SAFETY AT SIGNALIZED INTERSECTIONS

Two critical issues in transportation facing the United States are congestion and safety. Several trends in the relationship between quality and safety have been identified for non-intersection facilities, but the relationships for intersections has never been well defined. The purpose of this research is to examine the relationship between the operational quality of service and the level of safety at one specific signalized intersection. When analyzing the operational quality of a signalized intersection, the 1994 Highway Capacity Manual evaluates performance through two measures, volume-to-capacity ratio and average delay. This research focused on the relation between average stopped delay and safety. Preliminary investigation into the relation between traffic conflicts and delay indicates that average stopped delay for the entire intersection significantly affects total conflict frequencies, and that total conflict frequency increases as average stopped delay increases from 7 to 18 seconds/vehicle. The results also suggest that average stopped delay significantly affects slow vehicle and lane change conflicts, and that these conflict types decrease as average stopped delay increases from 2 to 20 seconds/vehicle.