Empirical models for estimating capacity and delay at stop-controlled intersections in the United States.

This paper reports on a series of research studies that have been conducted in the United States on stop-controlled intersections between 1987 and 1991. The two major objectives of these studies have been to develop a data base for traffic operations data at stop-controlled intersections and to develop a set of models that can be used to forecast capacity and delay at stop- controlled intersections. Empirical models have been developed for all-way stop- controlled (AWSC) intersections to estimate capacity and delay. The capacity model states that the capacity of a given approach is a function of the distribution of the volume among the intersection approaches, the number of lanes on each intersection approach, and the turning movement proportions on each approach. The delay model states that the average stopped delay on a given approach is a function of the volume/capacity ratio for that approach. A set of level of service ranges based on stopped delay has also been proposed. These two models form the basis for a new set of interim capacity materials recently adopted by the Committee on Highway Capacity and Quality of Service of the Transportation Research Board (TRB). Empirical models have also been developed for two-way stop-controlled (TWSC) intersections to estimate capacity and delay. The capacity model states that the capacity of a minor street approach is a function of the flow rate on the major street, the flow rate on the opposing minor street approach, and the speed of traffic on the major street. The delay model includes two components, one for service time and one for queue time. Both are exponential in functional form. The service time on the minor street approach is a function of the flow rates on the major street and on the opposing minor street approach. The queue time on the minor street is a function of the flow rate on the subject minor street approach. These models are preliminary and further study is now underway to determine the effects of capacity and delay of turning movements on each approach and the degree of platooning on the major street.