高架道路下匝道衔接交叉口U-turn设计方法

U-Turn Design for Elevated off-ramp Joined Intersection

高架道路下匝道地面衔接路段及其衔接交叉口的交通设计是城市快速路交通设计的一个重要组成部分,为解决我国城市高架道路下匝道与地面道路衔接交叉口排队和拥堵日益严重的问题,分析了U-turn设计对交叉口车辆延误和饱和度等运行效益指标的影响,以及U-turn在改善交叉口交通安全性方面的作用。以"变交叉为交织或避免交叉和交织"为目标,分析了高架道路下匝道不同接地类型与不同U-turn形式的最佳结合方法;以交叉口延误与左转交通流路段延误加权最小为目标的最佳U-turn选择模型,给出了高架路下匝道交叉口和路段两种U-turn的设计方法。最后,以上海市某高架道路下匝道及其衔接交叉口为例进行算例分析,实施U-turn设计后,可以显著降低交叉口的饱和度,最大降幅达29%;交叉口的车均延误最大降低60%,交叉口服务水平由D级上升到C级。

Traffic design of roads and intersections connected by grounded elevated off-ramps are a significant component of urban expressway design. To moderate the daily worsening of traffic queuing and congestion on urban elevat- ed off-ramps, the effect of U-turn design on vehicle delay, intersection saturation and other operation performance indices is analyzed, as is the role of U-turn design in improving the safety at intersections. Then two kinds of U-turn designs are presented, and, with the goal of ＂changing crossover to weaving or avoiding crossover and weaving＂, the techniques of optimizing a match between elevated grounded off-ramps and U-turn design in their respective different forms are discussed. Two methods of U-turn design are also given for intersection and road section to choose the best U-turn model for minimizing the weighting delay between intersection and left-turn roads. At last, as an example, an urban elevated off-ramp region in Shanghai is analyzed. After U-turn design, the saturation at the elevated off-ramp region decreased by 29%, with average delays decreased 60%, and the level of service improved from D to C.