Research On Capacity Of Left-turn Lanes At Signalized Intersection

Signal intersections are the main sites of a city for traffic conflicts and theircapacity restrict the capacity of the whole road network of the city. Based on thesurvey data, this paper aims to report some findings of traffic characteristics, capacityand key factors affecting capacity in left-turn lanes at signalized intersection by usingtheoretic analysis and computer simulation technology.For exclusive multi-strip left-turn lane with outside trap lane, based on thesurvey data in Beijing, traffic flow characteristics of left-turns are studied by usingstatistical methods. It shows that the discharge headway and saturation flow rate ofexclusive triple left-turn lane with outside trap lane divides into two stages when thedischarge time of vehicles in the left-turn bay is less than the left-turn green time. Thisresearch analyzes the effects of relationship between the length of left-turn bay andgreen time on the left-turn capacity. A theoretic model for left-turn capacity wasdeveloped by considering this characteristic. The developed capacity model will bevalidated on the basis of VISSIM simulations of a real-world signalized intersection.And the results demonstrate that the proposed capacity models well estimate theleft-turn capacity at signalized intersections in the case in which the length of left-turnbay and green time is not well optimized and well reflect the capacity loss due to thetransitional area bottleneck. For left-turn lane with waiting area，first, the trafficoperating process of left-turn lanes with waiting area was analyzed, and a capacitymodel for it was developed by the theory of saturation flow rate. Then, lost time wasfixed by the linear regression method. Finally, it find that the increased range ofleft-turn capacity with waiting area is related to the length of waiting area and losttime. For the left-turn lanes which allows the vehicles to turn around, the trafficoperating process of it was analyzed. According to the measured data, the saturationheadway of vehicle for different shift is analyzed using the T-test statistical method.And it found that there is a significant difference between the saturation headway ofthe left-turn and U-turn vehicles; then, a theoretic model for through-right turn lanescapacity was developed by saturation flow rate correction theory and probabilitymethods,The results provides a theoretical basis for planning, design, transformation,traffic organization, signal timing traffic, operations evaluation and lane setting atsignalized intersections.