为给交叉口交通组织设计提供理论依据，研究了直接左转和右转－前行－掉头两种左转交通流组织方式下的交叉口整体延误特性． 在韦伯斯特延误模型、可插入缝隙理论的基础上，通过数学推导，建立两种交通流组织方式下的车辆平均延误模型，以及左转交通组织方式的判别模型． 研究结果表明，以交叉口整体延误为优化目标，当左转流量小于某个阈值时，右转 － 前行 － 掉头方案较优;反之则直接左转方案更为合理;判别阈值与左转和对向车流流量的相对关系有关． 文中还选取典型十字交叉口为分析对象，进行延误参数的理论计算，同时通过 VISSIM 仿真获取仿真延误参数． 结果表明，理论计算与仿真结果基本一致，所提出的模型具有较高的准确度和可靠性．

In order to provide theoretical basis for the traffic organization design of intersections，the whole delay characteristics of intersections under two kinds of left-turn traffic flow organizations，namely，the direct left-turn plan and the right-turn-straight-U-turn (Ｒ-S-U) plan，are analyzed in this paper． Based on the Webster delay model and the gap acceptance theory，the vehicle average delay models for the two kinds of traffic flow organizations and a discriminant model of the left-turn traffic flow organization are constructed by means of mathematical derivation． It is found that，with the whole intersection delay as the optimization objective，the R-S-U plan has more advantages when the left-turn traffic flow volume is smaller than a certain threshold; otherwise，the direct left-turn plan is more reasonable． The threshold of flow discriminant is related to the relationship between the left-turn traffic flow volume and the opposite direction traffic flow volume． Finally，the theoretical delay parameter of a typical intersection is calculated，and the simulation delay parameter is obtained through VISSIM． The results show that the theoretical calculation results are consistent with the simulation ones，which means that the constructed models are of higher accurate and reliable．