协同自适应巡航控制车辆占比对下匝道分流区混合交通流安全性的影响分析

在人工驾驶车辆、自适应巡航控制（ACC）车辆和协同自适应巡航控制（CACC）车辆的行车行为特征分析的基础上，运用跟驰模型和换道模型分别构建人工驾驶车辆、ACC车辆及CACC车辆在下匝道分流区混合交通流仿真环境，解析CACC车辆占比对混合交通流安全性的影响。选取全速度差模型、ACC跟驰模型、CACC跟驰模型分别作为人工驾驶车辆、ACC车辆、CACC车辆的纵向跟驰模型，利用随意换道模型、强制换道模型分别构建下匝道分流主线段、远近端区的横向换道模型。基于碰撞时间（TTC）、暴露碰撞时间（TET）、整合碰撞时间（TIT）等参数构建交通流安全性评价指标。利用MATLAB进行数值模拟，仿真分析不同CACC车辆占比下的混合交通流安全性。结果表明:CACC车辆占比为40%~50%时，混合交通流安全性恶化最严重，TET和TIT分别增加约68%和89%，车辆速度离散系数为0.9以上；通过在下匝道分流区设置远端强制换道区（设置长度≤ 1 000 m），可有效降低混合交通流的追尾碰撞风险。 

An Impact Analysis of the Proportion of Adaptive Cruise Control Vehicles on the Safety of Mixed Traffic Flow at the Off-ramp Diverging Area

Based on the analyses of driving behavior of manually operated, adaptive cruise control(ACC), and cooperative adaptive cruise control(CACC)vehicles, this paper investigates the impact of proportion of CACC vehicles on the safety of mixed-traffic-flow at off-ramp diverging areas in a simulated environment, which is established based on a car-following model and a lane-changing model. Specifically, a full velocity difference model, an ACC car-following model and a CACC car-following model are used as the longitudinal car-following models for manually operated, ACC, and CACC vehicles, respectively. A discretionary lane-changing model and a mandatory lane-changing model are customized to develop the lateral lane-changing model for all types of vehicles at the main and end sections of off-ramp diverging areas, respectively. Next, a set of evaluation indices for traffic safety are proposed based on the following parameters such as time-to-collision(TTC), time exposed time-to-collision(TET) and time integrated time-to-collision(TIT). The MATLAB software is used to analyze the safety for mixed traffic flows under the scenarios with different proportions of CACC vehicles. The results show that: when the proportion of CACC vehicles ranges between 40% and 50%, the safety of mixed traffic flow deteriorates most, TET and TIT increase by about 68% and 89%, respectively, and the speed dispersion coefficient is as large as more than 0.9. Study results also indicate that the risk of rear-end collision for mixed traffic flow can be effectively reduced by adding the mandatory lane-changing area(≤ 1 000 m)at the far-end of off-ramp diverging area.