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 (g_f) and block the through vehicle is important when evaluating the queue accumulation polygon (QAP). If the process to determine the g_f 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. g_f 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 g_f, 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.