CAPACITY AT SIGNALIZED INTERSECTION APPROACH WITH A SHORT

The paper presents the findings of a study on the development of a capacity model for a signalized intersection approach with a short right-turn lane. The model takes into account of the stochastic nature of traffic flow and the effect of queue blockage to the short right-turn lane. The proposed model provides enhancements to the current Highway Capacity Manual methodology where the short-lane issue has not been addressed. The research showed that the capacity of a signalized intersection approach with a short right-turn lane is strongly related to the length of the right-turn lane, the proportion of through or right-turn vehicles, and cycle length. The study also found that CORSIM, the simulation model used in the model validation, yields higher saturation flow rates for the single lane section (i.e., the point where the right-turn lane splits) when a short right-turn lane is present. Such a flow-discharging characteristic is perhaps due to the nature of car-following models. Based on the case tested, the capacity enhancement with a short right-turn lane ranges between 5 to 19 percent compared to the shared-lane situation. Such capacity enhancements are contributed by both the short-lane usage and the increased saturation flow rate from the single-lane section. The proposed model yields capacity enhancement results within 1 percent error compared to the results from CORSIM