A Rational Method for Setting All-Red Clearance Intervals

The all-red clearance interval at traffic signals is designed to resolve conflicts and potential collisions between vehicles on opposing signal phases during the change period. This article describes a policy and procedure for setting the all-red clearance interval. This policy is based on physical and legal laws, observed driver behavior and previously developed analyses describing the dilemma zone concept. Based on the findings from this study, the authors recommend that the all-red clearance should take into account that the clearing vehicle is at the slow end of the speed distribution and that conflicting vehicles may be entering the intersection with a rolling start. It should also consider the most critical conflicting vehicle paths between these two vehicle types. Since entry into the intersection is legal up to the last instant of yellow, all-red clearance should be set without regard to the accompanying yellow clearance. The all-red clearance timing must reflect actual driver behavior and actual time-space paths of vehicles in a signalized intersection. An evaluation of the effectiveness of the proposed all-red clearance procedure indicates that it is successful in reducing collisions, injuries and fatalities.