公路接入口处驶入车辆换算系数估算方法

A Method for Estimating Conversion Coefficient of Vehicles Entering Highways’ Accesses

作为道路通行能力以及服务水平分析的关键参数之一,车辆换算系数的估算至关重要。我国现有路网尚未将接入道路纳入到技术等级体系,缺乏相应的设计规范和技术标准,接入口通常对公路路段的交通运行产生较大影响。基于公路接入口处不同类型的车辆特征,首先分析了接入口处的车辆在驶入公路路段过程中,在各种交通流状态下利用车道时间和空间资源的物理涵义。进而,以小客车作为标准车型,分别提出了公路路段上的车辆、接入口处驶入车辆的换算系数估算模型。最后,采用无人机航拍采集交通流运行数据,以郑州市G107上含多种车型的某路侧接入口为例进行了实证分析。结果表明:(1)随着路段上交通流量的增大,各驶入车型的车辆换算系数逐渐增大;且在驶入过程中所占用的车道数越多,相应的车辆换算系数值越高。(2)随着路段上交通流速度的增大,各驶入车型的车辆换算系数呈现出先增大后降低的趋势,且在速度值的40 km/h左右处分界。主要是由于交通流在稳定流状态时,车头间距亦介于自由流时的车头间距和饱和流的车头间距之间,此时接入口处的车辆在驶入公路路段时较为方便,但往往对公路路段上连续的多辆车同时产生影响,故此时的车辆换算系数值亦相对较大。

As one of the key parameters for analysing road capacity and service level,the estimation of conversion coefficient of vehicles are important.The domestic existing road network has not yet included access roads into the technical grade system and lacks corresponding design specifications and technical standards.Access points often have great influences on traffic operations of highway sections.Based on the characteristics of different of vehicle types at highway accesses,the physical significances of utilizing space-time resources of lanes under different traffic flow statuses when the vehicle at the access point entering highway section are analyzed.Furthermore,taking the passenger car as the standard vehicle,the models for estimating conversion coefficients of vehicles at highway section and access point are proposed respectively.Finally,the traffic flow operation data are collected by using UAV aerial photography.An access point on Zhengzhou G107 with multiple vehicle types is used as an example for empirical analysis.The results shows that(1)The conversion coefficient of each entering vehicle type increases with the increase of the traffic flow on the highway section.The more lanes occupied during the entering process,the higher the vehicle conversion coefficient.(2)The conversion coefficient of each vehicle type increases first and then decreases with the increase of the traffic flow speed on the highway section,showing a boundary around 40 km/h.That is because,in the steady flow state,the headway is between that of the free flow and that of the saturated flow.The vehicles at the access point are more convenient to drive into the road section,but it often has an influence on the continuous vehicles on the road section at the same time,so the value of vehicle conversion coefficient is relatively large.