Cycle-Length Performance Measures

Webster's single-ring formulation for cycle length and the Highway Capacity Manual (HCM) intersection saturation metric are revisited, and the model for dual-ring operation is extended to provide a tool for evaluating the effectiveness and efficiency of a prescribed cycle length. The calculations from Webster's model and the HCM provide a framework for identifying periods of time when cycle length could be substantially shortened, periods of the day when an increase in cycle length would provide some modest improvements, and periods of the day when cycle length is adequate and capacity problems should be addressed by adjusting splits. The methodology is demonstrated for incorporating the number of split failures, overall intersection saturation, and Webster's optimal cycle length to evaluate the quality of split operation and the effectiveness of cycle length at a signalized intersection.