Present and future assisting systems are meant to support the driver in coping with the difficulties of driving. The design of the system properties and their limits helps to influence on the road-driving behaviour directly and through teach-back effects. On the other hand there is a potential risk of negative effects on the safety due to a division of tasks between the driver and the technical system. Bearing this in mind, the Automotive Engineering Department and the Department of Ergonomics of Darmstadt University of Technology were engaged by BMW AG to investigate the distance behaviour of vehicles with and without ACC (Adaptive Cruise Control) which is used to control the speed and distance maintained to vehicles ahead and turning into the traffic.

This trial was made with the aim of a representative and objective investigation of the behaviour of the total system of driver-vehicle-environment in road traffic. A total of 50 rides were made on select routes which were carefully analysed with regard to relevant characteristics such as road type, number of lanes and speed limits. In order to avoid any acclimatization problems the testing persons were familiar with the used vehicle type and were selected on the basis of typical distribution of age and mileage travelled. Special emphasis was put on an even distribution of driving experience with and without conventional cruise control. In addition to the video equipment necessary for recording the traffic situation, the test vehicle was fitted with extensive equipment to record the actions of the driver, the driving parameters and distances and speeds relative to the road users ahead. The complexity of traffic situations necessitated classification in advance. The classification with regard to comparable situations was made, for instance, by means of videos which, in connection with the vehicle data, also served to define the characteristic moments of time and relevant parameters.

On this basis an objective analysis of distance behaviour is made from the safety aspect. The comparison drawn between the actually set and the specified distances reveals the conflict of aims between the compliance with legal regulations and actual traffic conditions. The driver’s behaviour, shaped by their personal motivation differs from the characteristics of the system. Potential methods are sketched out for improving traffic safety by using ACC.