Effects of ACC and CACC vehicles on traffic flow based on an improved variable time headway spacing strategy

An improved variable time headway (VTH) spacing strategy for the adaptive cruise control (ACC) and cooperative ACC (CACC) system is proposed. On the basis of the novel strategy, the typical two-modes of ACC/CACC upper-level controller are redesigned. Numerical simulations for two traffic scenarios are performed to verify the efficiency of the improved strategy. The results demonstrate the suitability and advantages of the improved VTH strategy in comparison with the constant time headway strategy and the VTH strategy. Furthermore, the authors study the impact of ACC and CACC vehicles on traffic flow by multiple-types mixed scenarios: ACC/manual vehicles, CACC/manual vehicles and ACC/CACC/manual vehicles. The results illustrate that introducing the ACC/CACC vehicles into mixed traffic can improve traffic flow stability, enhance road capacity and alleviate the increasingly serious traffic congestion problem.