Revisiting the Cycle Length—Lost Time Question With Critical Lane Analysis

During oversaturation, a popular objective in traffic signal operations is to maximize throughput in order to keep traffic moving. As cycle lengths are increased, the proportion of " lost time " used to transition between signal phases is reduced. This is often a rationale for programming long cycle lengths into signal timing plans. To investigate the impact of cycle length, this paper revisits the concept of critical lane analysis to calculate throughput, and applies the technique to data collected at an oversaturated intersection in Indianapolis, Indiana. Traffic volumes were measured from over 10 weeks while different cycle lengths were tested at the intersection, ranging from 80 to 135 seconds. Somewhat surprisingly, during saturated conditions, no clear increase in the sum of critical lane throughput was observed, even when the cycle length increased by over 50%. In fact, there was a slight reduction in the total critical lane sum volume at 135 seconds. The findings concur with a recent study by Denney et al.. The decrease in throughput under the longer cycle lengths is attributed to the reduction of saturation flow during long green times. The paper discusses possible results of using a time-dependent saturation flow rate. Additionally, the critical lane analysis methodology may have applications for agencies to evaluate and rank intersections within corridors as under, near, or over saturation. Day et al.