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以可接受间隙理论和排队论为基础,利用概率论的方法,对无信号T型交叉口左转车的交通特性进行分析。建立了左转车流的服务率模型，及被对向直行车阻断且其后有直行车到达的左转车到达率模型。然后将两者引入排队系统修正判断无信号交叉口是否需要设置左转车道的概率模型,算出了一定左转率对应的临界车流量组合，并绘制了判断是否需要设置左转车道的临界车流量组合曲线。利用此曲线可判定无信号T型交叉口是否需要设置左转车道，对无信号交叉口的规划、设计、建设和管理等工程实践具有重要的指导意义。

Analysis of Left-Turn-Lane Warrants at Unsignalized T-Intersections

Based on the gap acceptance theory and queuing theory,traffic characteristics of left-turn vehicles on the unsignalized T-intersections is analyzed with the probability theory.The service rate model of the left-turn vehicles on the unsignalized T-intersections has been set up,and the arrival rate model of the left-turn vehicles which are blocked by the opposing through vehicles and followed by one or more advancing through vehicles has also been set up.Given them in the queuing system,the probability-based model of justifying a left-turn-lane at the unsignalized T-intersections is modified.The paper has calculated the critical volume combinations of some left turn rates and drawn the critical volume combinations curves,which can be used to justify a left-turn-lane at unsignalized T-intersection.These curves have instructional significance on engineering practice of unsignalized intersection,such as planning,designing,constructing and administrating.