Average Delay at an Unsignalized Intersection with Two Major Streams Each Having a Dichotomized Headway Distribution

The average time a driver has to wait before he can cross two major streams has been a major performance indicator for unsignalized intersections. The equations presented in this paper give an estimate of this average delay as a function of the average delay to isolated minor stream vehicles (Adams' delay) and the degree of saturation of the minor stream (minor stream entry flow/maximum entry flow) and a form factor (which quantifies the effect of queueing in the minor stream). It was assumed that drivers were consistent and homogeneous and that headways in each major stream were independent of other headways in the same stream and in the other stream. Although the concepts were described in general terms, equations for the maximum minor stream entry flow and Adams' delay were developed assuming that the headways in the major stream to have a dichotomized distribution as given by R. J. Cowan in 1975. Tanner's equations can be used to calculate the form factor when there is a single major stream and when the minor stream headways are Poissonian. For other conditions, a computer simulation program was used to give estimates of the form factor which give satisfactory estimates of average delay for practical purposes. The discussion in this paper indicates that the degree of bunching in the major streams has a major effect of Adams' delay, average delay and the maximum minor stream entry flow.