Study On Capacity Of Left-turn Traffic In Signalized Intersections

As a vital component of urban roadway network, signalized intersection plays animportant role in road connection and operation. At signalized intersections, left-turntraffic produces the most number of conflicts, delays and accidents, which seriouslyaffects road safety and efficiency. Thus, left-turn traffic has become the key anddifficult point in the management and organization of signalized intersections. Thestudy of capacity of left-turn traffic can not only be used as the main basis ofintersection planning, design and operation management, but also promote thedevelopment of basic theories of traffic engineering.According to different control modes of signalized intersections, this paperstudies left-turn capacity under protected and permitted left-turn phase respectively.First, this paper summarizes the research actuality from three aspects: intersectioncapacity, left-turn capacity under protected left-turn phase, and left-turn capacityunder permitted left-turn phase. Up to13signalized intersections in Beijing whichhave different left-turn control modes are investigated, and then traffic characteristicsas well as organizational characteristics of left-turn traffic are studied under thecombination of on-site observation and statistic analysis. For left-turn traffic underprotected left-turn phase, the relationship model between number of lanes andsaturated headway is built by statistical analysis. Then, based on stop-line methodwhich is put forward by China, the capacity models of left-turn traffic under simple ormultiple left-turn lanes, left-turn lanes with waiting area and left-turn lanes whichallows U-turn are built respectively. For left-turn traffic under permitted left-turnphase, three ways for left-turn vehicles crossing the intersection are discussed, and thecapacity for left-turn vehicles using the accepted gap of opposite through vehicles tocross the intersection is mainly studied using probability theory and gap acceptancetheory. On the basis of observations and statistics, a large number of accepted gapsand rejected gaps are collected, resulting in that the critical gap of left-turn vehicles is3.9s using Raff’s method and Ashworth’s method, then capacity model is built and thetotal left-turn capacity will be finally obtained. In addition, there is a typical exampleafter each capacity model which can help a better understanding.