快速路匝道合流区流量、加速车道长度与通行能力关系

Relationship between acceleration lane length, flow and capacity in the urban expressway ramp merging section

为确定不同流量条件下城市快速路匝道合流区加速车道的合理长度及其通行能力,从匝道车辆汇入概率出发,基于间隙接受理论,分析匝道车辆在加速车道上等待汇入的速度和车速调整所需的时间,考虑车辆汇入带来的主线外侧车道不同位置流量变化及汇入失败概率,厘清流量、加速车道长度与通行能力之间的关系。研究结果表明:目前有关规程提供的加速车道长度偏短;匝道车辆汇入概率并不总是与主线外侧车道流量呈反比,在高于1600pcu/h时反而会呈正比;主线外侧车道流量在1 300~1 500 pcu/h时最易形成通行瓶颈,应采用匝道控制、主线车流引导或车道设计等方式解决。掌握好三者之间的关系对优化加速车道设计和匝道流量控制具有重要意义。

In order to determine the reasonable length of speed lanes and its corresponding capacity in the merging sections of urban expressway under different flow conditions. Based on the gap acceptance theory and starting from the merging probability of ramp vehicles, a calculation method of speed lane length and capacity of ramp merging section of urban expressway under different mainline and ramp flow conditions was established by considering four types of influencing factors, including the speed of ramp vehicles waiting merging, the required time to adjust for merging, changes in the traffic volume of the outer lane of the main line because of merging, and acceptable merging failure probability. Relationships between speed lane length, flow and capacity were clarified. The analysis results show that the values of speed lane length specified for design of urban expressway are smaller than the reasonable value. Although the probability of merging is inversely proportional to the traffic volume of outside lane, the probability of merging would increase with the growing traffic flow when the traffic volume of outside lane of the main line increases to 1 600 pcu/h. When the traffic flow of the outer lane of the main line is from 1 300 to 1 500 pcu/h, the bottleneck is most likely to occur, which should be solved by ramp control and traffic flow guidance of the main line or lane design. Mastering the relationship between the three factors is of great significance to optimize the design of acceleration lane and ramp control.