Determine Left Turn Capacity in Signalized Intersections Using Modeling and Simulation of Traffic Flow

The performance of traffic signal is to develop phasing plans that reduce delays while maintaining a high level of safety. In the signalized intersections and among various feasible movements, “left-turn” is the most complex and time-consuming, which can operate as a protected movement, a permitted movement and a combination of protected-permitted movement. The compilation of the required data for a significant number of variables for calculating the left-turn capacity at the signalized intersections is not possible by the time-consuming way Highway Capacity Manual (HCM) method and is not feasible for rapid decision-making. Therefore, identifying variables more effectively and finding a quick method in this regard is a research issue. So the main objective of this study is to investigate the factors affecting the left-turn capacity and it proposes a simplified model with the fewer number of variables rather than the material of HCM to determine left-turn volume. In this research, data of two signalized intersection in the city of Isfahan, Iran have been used. With these information’s a simplified single variable logarithmic model is proposed to determine left-turn capacity based on following factors opposing volume, number of lanes and percentage of green time. This model estimate critical left-turn capacity for protected left-turn phasing. To validate the objective model, a comparative assessment is carried out taking computational relations of HCM into account. At the end of the research the modeled intersections are simulated by AIMSUN software and the left-turn capacities are obtained in permitted phasing given various indices.