Investigation of saturation flow on shared right-turn lane at signalized intersections

Saturation flow rate is regarded as one of the key parameters in estimating capacity and delay for the evaluation of performance at signalized intersections. In China, the saturation flow rates of shared right-turn lanes typically show large fluctuations hecause of the different departure characteristics of through and right-turning traffic, as well as complex interactions with pedestrians. This study addresses this complexity by proposing a four-stage saturation departure model based on an empirical analysis of discharge headways in shared lanes. The developed model reflects the stochastic nature of vehicle-pedestrian conflict and constructs the logical relationships between shared right-turn saturation flow and its various influencing factors, such as right-turn proportion, pedestrian demand, and the storage capacity of the right-turn radius. A comparison of observed saturation flow rates and estimates from the proposed model and the Highway Capacity Manual demonstrates the good performance of the proposed method. The manual, however, is found to underestimate the effect of pedestrian interference on performed saturation flow rates.