Adaptive Cruise Control in Practice: A Field Study and Questionnaire into its influence on Driver, Traffic Flows and Safety

Adaptive Cruise Control (ACC) is a system present which enables the car to autonomously maintain a certain speed, and based on the location and the speed of the predecessor, change the speed of the vehicle. This research is meant to determine the influence of ACC on the behavior of the driver, and on flows and safety on the road. Three databases are used: a literature review, a questionnaire, and a Field Operation Test. The questionnaire, containing 56 questions, was distributed among as many ACC users as possible. This was done mainly with help of the Dutch Motorists’ Organization ANWB. In total 200 valid responses were collected from users with Adaptive Cruise Control experience, and 25 responses from a reference group without ACC experience. The field test consisted of eight participants. Their driving behaviour was analysed during normal use of their leased ACC-equipped car on the highway. In total these eight drivers provided 48 hours of driving data. The recording was done by two cameras: one facing the road in front of the vehicle, and one facing the dashboard to record the ACC settings. Also a data logger was installed in the OBD-II port of the cars, recording speeds. The results of these three databases provided an overall analysis of the influence of ACC on the driver, on traffic flows and on safety. ACC leads to larger headways, but also to more constant speeds and headways, less lane changes and more car-following driving behaviour. This results in more homogeneous traffic. These characteristics enable ACC to prevent shockwaves and head-tail collisions. ACC leads to more relaxed driving and a relief of the driving task. Two third of the drivers indicates that this does not lead to a decrease of attention level, but another third does indicate they loose attention when driving with ACC. Half of this group uses this opportunity to perform more secondary activities. Preparation before using ACC is very important, since prepared users do encounter unexpected situations when using ACC less often. Also they use ACC more prudent: they do perform less secondary activities and stay alert. 22% of the respondents of the questionnaire did not receive any instructions at all. They learn to operate ACC by using it in practice. They show less insight in the risks of using ACC. This means this group might use ACC in an unsafe way. ACC systems which are active at all speeds are rated more positive compared to systems with a lower limit. Despite that, all systems, regardless of their range, are barely used on rural and urban roads. ACC is a system most fitted to be used on highways. Users tend to get used to ACC quite quickly and are willing to accept the working of ACC, despite it not always performing well. They seem to easily adapt to using ACC. This is hopeful for the further development of improved ACC systems and other ADAS-systems. ACC is less intelligent: it only looks to one predecessor. Therefore its driving style is sometimes too defensive (it brakes much too early) and sometimes too offensive (it breaks too late). Other safety risks are in the lack of preparation of some users, resulting in an invalid assessment of the risks of using ACC. Preparation before using ACC is important to guarantee safe usage, and a proper assessment of the risks by the user. Therefore instructing drivers beforehand increases safety. ACC has a positive influence on traffic stability, but the headways increase very much. By designing an ACC system which looks further ahead than only one car, the average headway can safely be decreased. The car will be able to anticipate on its predecessors and the surrounding traffic much better. Even better is Cooperative ACC, where communication exists between different cars, which leads to even more stable driving behavior.Transport & PlanningCivil Engineering and Geoscience