Red Clearance Intervals: Theory and Practice

At signalized intersections the red clearance interval has to be long enough to prevent accidents but not longer than necessary to ensure efficient traffic operations and encourage respect for the red indication. Because designers used a variety of methods to calculate clearance times, the association of Dutch traffic control engineers (Contactgroep Ver-keersregeltechnici Nederland) initiated the development of a generally applicable method. The resulting method is based on a driver behavior model that involves five parameters. In contrast to the suggested Institute of Transportation Engineers (ITE) method, it determines red clearance time for each ordered pair of conflicting streams depending on the distance of the entering and exiting streams from the zone in which the two streams' paths overlap. The conflict zone method was calibrated by using field data collected at two intersections and was included in the 1996 Dutch guidelines for traffic controllers. In comparison with the ITE-suggested method, which gives the exiting stream enough time to clear the entire intersection, the new method is sensitive to the sequence in which traffic streams appear in the cycle and tends to call for less clearance time, improving intersection capacity and reducing delay. This approach is especially beneficial in improving efficiency of intersections with actuated control.