Evaluation of Impacts of Adaptive Cruise Control on Mixed Traffic Flow

This paper addresses the impacts of Adaptive (Intelligent) Cruise Control (ACC) laws on the traffic flow. Semi-automated vehicles, such as ACC Vehicles, with the capability to automatically follow each other in the same lane, will coexist with manually driven vehicles on the existing roadway system before they become universal. This mixed fleet scenario creates new capacity and safety issues. In this paper, simulation results of various mixed fleet scenarios under different ACC laws are presented. Explicit comparison of two ACC laws, Constant Time Headway (CTH) and Variable Time Headway (VTH), are based on these results. It is found that the latter one has better performance in terms of capacity and stability of traffic. Throughput increases with the proportion of CTH vehicles when flow is below capacity conditions. But above capacity, speed variability increases and speed drops with the CTH traffic compared with manual traffic, while the VTH traffic always performs better. Introduction Ideally semi-automated vehicles, such as Adaptive (Intelligent) Cruise Control (ACC) Vehicles, with the capability to follow each other automatically in the same lane will improve traffic flow on existing roadways. Research on the properties of automatedvehicle platoons has shown the potential benefits for capacity and safety (Van Arem et al. 1996; Broqua et al. 1991; Minderhoud and Bovy 1998). It seems an appealing scenario that all of vehicles fall under the protection of advanced automation technologies. But, it is more reasonable to imagine that semi-automated vehicles will coexist with conventional manually driven vehicles at the initial stage of deployment. A mixed control scenario raises complex capacity and safety issues that we must probe before ACC becomes reality. Previous research estimated the impacts of ACC in some specific situations (Van Arem et al. 1996; Broqua et al. 1991; Minderhoud and Bovy 1998). Their results are meaningful for the traffic operators to outline the potential impacts of ACC. However, the traffic flow characteristics that ACC will bring are difficult to quantify. And it is not possible to make direct comparison among these documents, because these studies have employed different ACC algorithms, different driver behavior models and a different driving environment. Our research will begin with the simplified scheme they used. On the other hand, more complex situations are simulated in our microscopic traffic simulation program. We will try to summarize the impacts of ACC from a large number of simulations in which some stochastic mechanisms make the results more realistic. Department of Civil Engineering, University of Minnesota, 500 Pillsbury Drive SE, Minneapolis, MN 55455; phone 01-612-625-4021; [email protected] 2 Department of Civil Engineering, University of Minnesota, 500 Pillsbury Drive SE, Minneapolis, MN 55455; phone 01-612-625-6354; levin03 [email protected]