Estimating reaction time in Adaptive Cruise Control systems

Vehicle automation and cooperation is progressively being introduced in traffic networks. As a consequence research to assess its impacts is currently ongoing. Adaptive Cruise Control (ACC) is one of the first automated functionalities available for privately owned vehicles. An experimental study has been conducted to investigate the key features of the ACC controller using Global Navigation Satellite System data. The first remarks based on the data focus on the controller's reaction time and desired time gap. Both parameters are essential in order to assess the influence of these technologies to safety and traffic flow. It is a common assumption that autonomous vehicles will have negligible reaction time and desired time gap comparable to that of a human driver. This paper presents an experimental study of an ACC -enabled vehicle on car following mode and a methodology for the estimation of the controller's reaction time that can be used as benchmark in other scenarios. The results show the reaction time to be around 1.1s and the time gap to be distinctly larger than that of a human driver. This poses concern on the impact of ACC on traffic flow when a significant number of vehicles will have such systems operating on -board.