Determining the Length of the Right-Turn Lane at a Signalized Intersection

Abstract

This paper develops the analytical and computational processes for determining the length of the right-turn lane at a signalized intersection. It examines the factors that influence the length, reviews the available literature and practices, derives the recommended length analytically, develops a set of tables of the recommended lane lengths as a function of the approach volumes (right-turn, through-traffic, and cross-traffic volumes) and signal timing, and discusses the results. The analysis is done for two cases: when right-turn-on-red (RTOR) is not permitted and when it is permitted. The probabilities of the following events are computed: the right-turn vehicles do not overflow to the through lane and block the movement of through vehicles, and the queued through vehicles do not block the entrance of the right-turn lane. The lengths are derived to keep these probabilities greater than a threshold value. The recommended length is shown in the number of vehicle spaces, and a procedure that converts this number to the actual distance is presented. The current guidelines for lane length are based on the arrival rate of right-turn vehicles only. The arrival rate of the through vehicles must be considered also. As a result, the proposed lane length is different than in the existing guidelines. In addition, a new guideline of lane length is developed for the RTOR case.