Probabilistic model for signalized intersection capacity with a short right-turn lane

The paper presents a capacity estimation model for a signalized intersection approach with a short right-turn lane. The proposed model overcomes one of the major shortcomings of the current capacity estimation methodologies by considering the probabilistic nature of traffic flow and the effect of queue blockage to the short-lane section. The research showed that the capacity of a signalized intersection with a short right-turn lane is strongly related to the length of the short lane, the proportion of through and right-turn vehicles, and cycle length. The study also revealed new findings, through simulation, on the saturation flow rate discharging from the single-lane section where the right-turn lane splits. It was found that the saturation flow rate increases with the increase of the length of the right-turn lane. The proposed model was validated against the results from CORSIM, a microscopic traffic simulation model, and found general agreement between the two results. Capacity enhancement is achieved with a short right-turn lane compared to the shared-lane situation. Such a capacity enhancement is contributed by both the short-lane usage and the increased saturation flow rate from the single-lane section. An example of a common application of the proposed model is to provide adequate design of the length of the right-turn lane so that the projected traffic demand can be accommodated at an acceptable service level while minimizing the cost associated with the construction of a full or longer right-turn lane.