An Analysis of the impact of Geometry Design to the safety of Interchange Ramps of Urban Expressways
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摘要: 由于城市快速路转向交通流量大、线形设计标准低,快速路立交匝道成为交通事故的多发点。利用上海市快速路3年事故数据和交通流量检测数据,以上海市浦西地区快速路立交匝道为研究对象,根据车辆在匝道上的行驶特征以及车辆交互特性,将立交匝道划分成出口段、衔接段和入口段及左转匝道、右转匝道等5个研究单元,针对各单元分别建立负二项模型分析匝道几何设计及其组合参数、交通流特征对于安全的影响。结果表明,出口段及入口段的安全性与几何特征的联系较为紧密;迂回式左转匝道相较于右转匝道受几何线形影响大;流量越大、长度越长,事故风险越高,但出口段的长度与事故发生呈负相关关系;出口处为直线、入口处存在长直下坡路段、入口处线形与主线差异大的立交匝道安全性差;迂回式左转匝道上存在过小半径曲线,特别是将小半径曲线设置在出口处,会极大增加事故几率。Abstract: interchange ramps of Urban expressways,serving a large number of turning flow and with a low design standard,are accident-prone.In order to evaluate the safety of interchange ramps,accidents data and traffic flow data in recent 3 years at Puxi Expressway in Shanghai are collected.Based on vehicle behavior and interactive features of vehicles on the ramps,interchange ramps are divided into 5 study units:exit segment,connecting segment,entrance segment, left-turn ramp and right-turn ramp.For each unit,a Negative Binomial Model is developed to analyze the relationship a-mong road geometry design features,their composite effect and traffic flow,and their impacts on safety.The results show that the safety of exit and entrance segments is closely related to geometry design.Compared with right-turn ramps, the left-turn roundabout ramps are more likely to be affected by geometry design.With a higher traffic flow or longer road segment,the risk of traffic accidents is higher.However,longer exit segments are safer.The ramps that have straight line at the exit,or have long-straight downhill section at the entrance,or have a large design difference between entrance and main segment,are less safe.There are more traffic accidents taking place on left-turn roundabout ramps with small radius curve,especially when the curve is located on the exit of ramps.
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