Comparison of delay estimates at under-saturated and over-saturated pre-timed signalized intersections

Abstract

Delay is an important parameter that is used in the optimization of traffic signal timings and the estimation of the level of service at signalized intersection approaches. However, delay is also a parameter that is difficult to estimate. While many methods are currently available to estimate the delays incurred at intersection approaches, very little research has been conducted to assess the consistency of these estimates. This paper addresses this issue by comparing the delays that are estimated by a number of existing delay models for a signalized intersection approach controlled in fixed-time and operated in a range of conditions extending from under-saturated to highly saturated. Specifically, the paper compares the delay estimates from a deterministic queuing model, a model based on shock wave theory, the steady-state Webster model, the queue-based models defined in the 1981 Australian Capacity Guide, the 1995 Canadian Capacity Guide for Signalized Intersections, and the 1994 and 1997 versions of the Highway Capacity Manual (HCM), in addition to the delays estimated from the INTEGRATION microscopic traffic simulation software. The results of the comparisons indicate that all delay models produce similar results for signalized intersections with low traffic demand, but that increasing differences occur as the traffic demand approaches saturation. In particular, it is found that the delay estimates from the INTEGRATION microscopic simulation model generally follow the delay estimates from the time-dependent models defined in the 1997 HCM, 1995 Canadian Capacity Guide, and 1981 Australian Capacity Guide over the entire range of traffic conditions considered.