Comparative Assessment of 1985 HCM Delay Model

Abstract

Delay is an important measure of effectiveness in traffic studies; it represents the direct cost of fuel consumption and indirect cost of time loss to motorists. The 1985 Highway Capacity Manual (HCM) used delay as the principal measure of level‐of‐service at signalized intersections. The manual introduced a delay model that is based partially on the traditional Webster model. The goals of this study were: (1) To review the delay models currently being used in the SOAP84 computer model for an isolated intersection and by the TRANSYT‐7F computer model for an arterial; (2) Compare them with the original model developed by Webster and the new model proposed by the HCM; and (3) assess the HCM model in both isolated intersection and urban arterial environments. The results show that the new HCM delay model is sensitive to arrival type; thus it is important to know which arrival type to use. The delay values calculated by the new HCM model, SOAP84, and TRANSYT are close to the values resulting from NETSIM.