Determination of storage lengths of left-turn lanes at signalized intersections

A new method has been developed for estimating the storage lengths of left-turn lanes at signalized intersections. To prevent lane overflow, the left-turn lane should be designed to have a length sufficient to store the longest expected queue. In this study, the left-turn queue length was estimated by considering two factors: (a) vehicles that arrive during the red phase and (b) the queue of vehicles carried over from previous cycles. A method based on the discrete-time Markov chain was applied to model the leftover queue length at the end of the green phase. A case study was provided to demonstrate the application of the proposed model. In the model evaluation, the estimated left-turn queue lengths were compared with field observations and estimates from other existing methods. The results showed that the proposed model significantly outperformed existing methods by providing more accurate estimates of the lengths of left-turn queues.