Time for a Left-Turner to Block a Shared Lane of a Signalized Intersection

Abstract

Frequently, signalized intersections have a single lane for both left-turners and through traffic. If the vehicles leaving this lane are opposed by through traffic, then no vehicles can depart after a left-turner reaches the head of the queue. This paper evaluates a single lane of left-turning and through vehicles in the subject stream and a single lane of through vehicles in the opposing stream. The first left-turning vehicle is delayed if the opposing flow is high and this further delays other vehicles in the subject stream. The time for the first left-turning vehicle to arrive at the stop line ( gf) and block the through vehicle is important when evaluating the queue accumulation polygon (QAP). If the process to determine the gf term is not well established and accurate, then all other aspects of QAP will not be accurate and the prediction of both capacity and delay will also be inaccurate. gf was determined through a theoretical evaluation to establish the form of the equation and simulation to establish empirical values for the parameters. The resultant equation had a standard error of 0.83 s. The proposed equation was compared with other expressions for gf, including the equation currently in use in the Highway Capacity Manual, and found to have a much lower standard error than those of other methods.