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 the 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-, and cross-traffic volumes) and signal timing, and discusses the results. The analysis is performed for two cases, when right-turn-on-red (RTOR) is not permitted and when RTOR 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 the through-vehicles, and the queued through-vehicles do not block the entrance to the right-turn lane. The lengths are derived to keep these probabilities greater than a threshold value. The recommended length is shown in number of vehicle spaces, and a procedure that converts this to the actual distance is presented. The current guidelines for the lane length are based on the arrival rate of the right-turn vehicles only. It is found that the arrival rate of the through-vehicles must be considered also. As a result, the proposed lane length is significantly different from the existing guidelines. In addition, a new guideline of lane length is developed for the RTOR case.
Abstract