Unsignalized Intersection Analysis: Effect of Overlapping Conflicting Traffic Flow on Minor Movement Potential Capacity

Abstract

A particular component of two-way stop unsignalized intersection analyses as presented in the 1994 Highway Capacity Manual (HCM) is described. Specifically, advantages to minor movement capacity are evaluated where traffic flows overlap in multiple lanes. From vehicular arrival data collected by the author, it was determined that the current HCM can significantly underestimate the true potential capacity of minor movements that face multiple lanes of free-flow conflicting traffic. A modification to the HCM procedure is introduced in which an “effective” conflicting flow is calculated on the basis of “blockage” caused by individual lanes of traffic, assuming a Poisson count distribution. In every case examined (24 total), a more accurate potential capacity estimate resulted relative to that determined by the HCM procedure. The modification also resulted in a more accurate level of service in 8 of the 24 cases.