Development of arrival/departure based uniform delay model for left-turn traffic at signalized intersections

Left-turn traffic may reduce operational efficiency and increase accident potential at signalized intersection, if it is not managed properly. Protected plus permitted left-turn phasing (PPLT) with exclusive left-turn lanes are commonly used to improve the operational efficiency at signalized intersections. However, only limited research has been done in evaluating operation quality for such phasing. Delay for PPLT is commonly estimated using the HCM method under the assumption of uniform arrival flow rate. This assumption does not take into account the effect of signal progression and platoon arrival and affects the accuracy in estimating the blocked time, left turn saturation flow rate as well as delay, especially for a coordinated signalized intersection.;This research developed mathematical models for estimating the uniform delay for protected plus permitted left turn traffic at signalized intersections by directly taking into account the effects of arrival type (platooning). The models use different flow rates for the vehicles within and outside the platoon for both the subject left lane and opposing approach. A general uniform delay model was derived to cover all combinations of left turn and opposing traffic arrival types. In addition, the study proposed a blocked time estimation method that is more accurate than the current method used in HCM. Furthermore, the study developed permitted left turn saturation flow rate models that depend on unsaturated opposing discharge flow rate during unblocked time.;Field data was collected to calibrate CORSIM simulation model. The calibrated CORSIM was used to generate scenarios covering all possible arrival types for both left turn and opposing through approaches. The comparison of the control delay from the proposed and HCM models to simulated field data from CORSIM indicated that the HCM model underestimate the control delay, but the proposed model was more accurate in estimating the delay for left turn lane group with PPLT.;The proposed models then were applied to real-time signal control system for coordinated intersections with protected-plus-permitted left turn phasing. Test results showed that the real-time signal control taking into account the left turn treatment and signal progression can improve the signal control effectiveness.