Signalized Intersection Turn Left

Intersections are bottlenecks of urban road network. In order to reduce the delay and start-up lost time, and improve the level of service and intersection's capacity, left-forbidden management is widely used at signalized intersections at arterials in Kunming, southwest of China. But it also brings a series of problems with the increasing use of left-forbidden management. Firstly, vehicles can fulfill left turn by right turn plus U-turn or U-turn plus right turn, but U-turn discharge headway is unknown, and bus headway distribution at left-forbidden signalized intersections is also unknown. Secondly, for a specific intersection whether it is supposed to forbid left turn with different period of time. Thirdly, for the purposes of keeping public transit priority, buses are allowed to make left-turn at left-forbidden signalized intersections in the condition of safety and don't be provided left exclusive phase, but the conflict delay of left bus is also unknown. This paper studies these aspects with field data in Kunming.First of all, the paper presents a study of discharge headway, including U-turn, through and left turn, with the field data which were collected with exclusive lane and protected phasing at median openings and intersections in Kunming. Based on the headway distribution analysis, the saturation headway and start-up lost time were calculated by analyzing mean and variance. The bus headway distribution is tested to study left turn bus's effect on bus headways which include subjective and opposing ones at left-forbidden intersection.Secondly, U-turn's control delay model was improved on the basis of Highway Capacity Manual (HCM,2000 version). The improved control delay model was more accurate which was compared with the results from HCM2000 and Design Regulations for At-grade Intersections on Urban Street (DRI), and it was proved by using the real-world observed data. Based on these conclisions, the paper also discusses whether the specific intersection is supposed to forbid left-turn with different period of time. Finally, the left turn bus conflict delay model is developed with different distribution of the opposing through vehicles'headways and the left turn bus's critical gap is given.The work which has been done in this paper will supply some reference for the relevant research and application in the future.