Effect of Through Movement Flow Rate on Left-Turn Lane Utilization at Signalized Intersections

Heavy left-turn volumes can increase the delay at any signalized intersection. This study aims to investigate the interaction between through movement and left-turning movement at signalized intersections. A microsimulation approach is employed to simulate real traffic conditions at a signalized intersection in the city of Doha, Qatar. Different scenarios with different traffic needs, left-turn bay designs, and traffic control parameters were used. For each scenario, the left-turn throughput, average delay, and average queue are recorded. The results indicated that the approach volume is influencing the level of utilization of left-turn lanes, regardless of the number of lanes or the storage length. The results also reveal that high delay at left-turn lanes is experienced as the through movements reach capacity. In regards to left-turn queues, while increasing the number of left-turn lanes has reduced the queue length, the associated high delays indicate that the storage bay is not fully utilized, and many of the left-turn vehicles are not allowed to enter the left-turn bay due to the through movement demand. The results indicate that through movement flow rate should be considered when deciding the number and length of left-turn lanes needed instead of focusing only on the left turn demand. The results also suggest that the use of microsimulation can provide more accurate results when determining the length and number of left-turn lanes.