Impacts of shorter perception-reaction time of adapted cruise controlled vehicles on traffic flow and safety

Auto manufacturers have begun to market an adaptive cruise control system (ACCS) as an option that promotes driver safety. This paper examines how the presence of vehicles equipped with ACCS affects stability and safety of a flow consisting of both ACCS and non-ACCS vehicles. We focus on the effects of the short perception-reaction time of the ACCS vehicles. Given a perturbation to the first vehicle in the platoon, the behavior of each following vehicle is tracked for changes in headway, speed, and location using a simulation model. A fuzzy rule based car-following model is selected as the test-bed for simulation after reviewing other models. Simulation is conducted under many scenarios with respect to the number of ACCS vehicles, the perception-reaction times, and the ACCS vehicle's placement in the platoon. We introduce two measures to evaluate stability and safety: one, the pattern of changes in the minimum spacing for each pair of two consecutive vehicles, and two, the total time during which the following vehicles cannot stop safely. It is found that, generally, the shorter perception-reaction time of the ACCS vehicles can shorten the process of achieving stability, and also can promote safety to both the ACCS and the non-ACCS vehicles under congested conditions. The findings generate an interesting debate on the issues of the benefits that non-ACCS vehicles enjoy as a result of the presence, of ACCS vehicles in the traffic flow.