Evaluating the Impact of Free Left Turns on Traffic Behavior at Signalized Intersections in Heterogeneous Traffic Conditions

Abstract

Traffic signals optimise efficiency and safety at intersections by separating conflicting traffic movements in time. To achieve the same vehicle throughput in a reduced signal cycle time, often free left turns are provided for left side driving traffic. The current study intends to evaluate the impact of these free left turns on the traffic behavior by i) measuring their existing capacity utilization and ii) establishing the various factors influencing their performance. Queue lengths and travel times of the left turning vehicles are taken as the indicators of their performance. VISSIM software is used for micro-simulation of traffic and from the results obtained, regression models are developed for queue lengths and travel times. Also, effect of a signalized left turn in place of a free left turn is estimated in terms of the alteration it causes on the queue lengths and travel times of left turning vehicles.