Evaluating the Traffic Impact of Eliminating Direct Left Turns at Signalized Intersections (Case Study: Golzar Intersection, Karaj City)

Urban signalized intersections, as one of the most critical nodes in transportation networks, play a decisive role in the traffic performance of cities. One of the management strategies employed to increase capacity and reduce traffic conflicts is the elimination of direct left turns and redirecting the corresponding flows through adjacent U-turns. This study aims to evaluate the impact of this policy on the traffic performance of the Golzar intersection in Karaj. Required data were collected through field surveys of traffic volume, geometric characteristics, and traffic signal timing during morning, noon, and evening peak hours. Saturation flow, density, time headway, and lost time indices were calculated and analyzed for different intersection approaches. The results indicated that eliminating direct left turns shifted a portion of traffic demand to adjacent U-turns; however, the overall performance of the intersection remained at an acceptable level during most time periods. Furthermore, the east–west axis experienced the highest traffic pressure and approached saturation conditions during the evening peak hours. The findings suggest that eliminating direct left turns can serve as a low-cost management strategy to improve the performance of high-traffic urban intersections, provided that the capacity and performance of alternative U-turns are simultaneously considered.