Evaluating the effect effects of U-turns on level of service of signalized intersections using synchro and SimTraffic

In this study, a procedure was developed to help transportation professionals evaluate the impacts of U-turns on level of service of signalized intersections using two widely used simulation packages: Synchro and SimTraffic. Two parameters related to U-turns were calibrated based on field data. They are (1) the saturation flow rate for U-turn and left-turn mixed traffic stream; and (2) the turning speeds for U-turning vehicles in the left-turn lane. The saturation flow rate was calculated based on the U-turn adjustment factors developed in a previous study. A linear regression model was developed for predicting the average turning speeds of U-turning vehicles at a signalized intersection given the turning radius provided at the left-turn bay. Delay reported by the calibrated Synchro and SimTraffic models was compared to the average control delay measured in the field. The effectiveness of parameter calibration differs for different signalized intersections. It was generally found that the calibrated Synchro and SimTraffic models provided reasonable delay estimates for U-turns at signalized intersections. With the calibrated and validated Synchro and SimTraffic models, sensitivity analysis was conducted to evaluate how the increased number of U-turning vehicles affects the level of service of signalized intersections. It was found that the sensitivity of the average control delay to changing U-turn volumes differs for different signalized intersections. The sensitivity analysis results suggest that the impacts of U-turns on the level of service of signalized intersections shall be evaluated on a case-by-case basis.