Developing an Analytical Model and Simulation of The Contraflow Left-Turn Lane at Signalized Intersections

Document Type : Research Paper


1 Assistant Professor, Department of Civil Engineering, Kharazmi University, Tehran, Iran

2 MSc Grad., Department of Civil Engineering, Kharazmi University, Tehran, Iran


At some intersections, excessive queue lengths may spill out of the left-turn bay and block the through lanes, jeopardizing level of service for the entire intersection. One of the most effective plans recently presented by the researchers is the "Contraflow left-turn lane" (CLL) In this method, left-turn vehicles will use the nearest lane in the opposite direction in addition to the usual left-turn lane. The most important principle in this design is that all vehicles which go into the opposite direction for left-turn movements should be definitely discharged during the left-turning phase. This issue prevents vehicles from a head-on collision when the other traffic signal turns green. Therefore, the number of vehicles entering the lane should be limited by a traffic signal. Accordingly, in this study, while determining the left turning capacity of the intersection with the CLL design based on vehicle traffic with generalized Poisson distribution, optimal CLL length and appropriate timing of the incoming traffic signal were determined. The goal of this study is to examine the effects of the CLL design on intersection performance. Therefore, the simulation of three real intersections in AIMSUN software was performed in two conventional and CLL designs. Comparison of the simulation results of the two designs showed that the CLL design at the intersections while reducing the travel time by 6 to 16 percent, resulted in an 8 to 24 percent reduction in vehicle delay. Also, according to the results of the study, the CLL scheme increased the number of stops for vehicles from 7 to 18%.


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