Evaluating the Operational Impact of Left-Turn Waiting Areas at Signalized Intersections in China

Abstract

Transportation professionals in China have started using left-turn waiting areas and lagging left-turn phasing to improve traffic efficiency at signalized intersections. Left-turn waiting areas are usually set up beyond the stop bar at an exclusive left-turn lane or dual left-turn lanes. This design allows left-turning vehicles to enter and wait at the left-turn waiting area after the initiation of the through phase. The operational impact of left-turn waiting areas at signalized intersections was evaluated, and the arrival and departure processes of left-turning vehicles at exclusive left-turn lanes with and without waiting areas were compared. A procedure for estimating the capacity of an exclusive left-turn lane with a waiting area was proposed. Cross-sectional analysis used data collected from 12 approaches at nine signalized intersections to compare the start-up lost time and saturation headways of left-turn passenger cars for four scenarios. The capacities of exclusive left-turn lanes with differently sized left-turn waiting areas were compared. The results indicate that left-turn waiting areas increase the capacity of exclusive left-turn lanes and that the capacity gains would increase with an increase in the storage capacity of the left-turn waiting area.