Overflow Delay Model for Signalized Arterials

Delay is the principal parameter used to measure the performance of signalized intersections. Average stopped delay is the primary measure of effectiveness used in evaluating level of service at signalized intersections in the U.S. Highway Capacity Manual (HCM). In an urban street network, the traffic performance at contiguous intersections is highly correlated. Typically, two upstream effects are present, signal coordination and signal metering. Therefore, the delay models developed for an isolated intersection with the assumption of random arrivals are no longer appropriate for delay estimation at a signalized arterial. The impact of signal coordination on delay has been well documented in the literature. However, the signal metering effect has yet to be thoroughly evaluated. For uncongested network flow conditions, the upstream metering effect is of less importance. However, for congested network flow conditions operating at or slightly below capacity, upstream metering becomes critical. In this study, an analytical overflow delay model that effectively incorporates the upstream metering effect for congested signalized networks is developed and the parameters are calibrated. The model is founded on a random queue model that assumes a generalized arrival distribution and a bulk service time distribution. The format of the overflow delay model developed in this work is consistent with the format of the current HCM model. The enhanced model, when effectively validated by field data, can be a good supplement for the current HCM model.