Driver's behavioral adaptation to Adaptive Cruise Control (ACC): The case of speed and time headway

• Two novel measurements were adopted to continuously assess the time headway.
• Real users of ACC were included in the study as participants.
• The ACC usage did not cause a negative effect on traveling speed.
• The ACC usage generated a positive effect on the observance of safety distances.
• ACC users and regular drivers differed about the observance of safety distances.

ProblemThe Adaptive Cruise Control is an Advanced Driver Assistance System (ADAS) that allows maintaining given headway and speed, according to settings pre-defined by the users. Despite the potential benefits associated to the utilization of ACC, previous studies warned against negative behavioral adaptations that might occur while driving with the system activated. Unfortunately, up to now, there are no unanimous results about the effects induced by the usage of ACC on speed and time headway to the vehicle in front. Also, few studies were performed including actual users of ACC among the subjects.ObjectivesThis research aimed to investigate the effect of the experience gained with ACC on speed and time headway for a group of users of the system. In addition, it explored the impact of ACC usage on speed and time headway for ACC users and regular drivers.MethodA matched sample driving simulator study was planned as a two-way (2 × 2) repeated measures mixed design, with the experience with ACC as between-subjects factor and the driving condition (with ACC and manually) as within-subjects factor.ResultsThe results show that the usage of ACC brought a small but not significant reduction of speed and, especially, the maintenance of safer time headways, being the latter result greater for ACC users, probably as a consequence of their experience in using the system.SummaryThe usage of ACC did not cause any negative behavioral adaptations to the system regarding speed and time headway.Practical applicationsBased on this research work, the Adaptive Cruise Control showed the potential to improve road safety for what concerns the speed and the time headway maintained by the drivers. The speed of the surrounding traffic and the minimum time headway settable through the ACC seem to have an important effect on the road safety improvement achievable with the system.