This report describes a field experiment that was conducted to investigate driving behaviour in approach and car-following manoeuvres. The aim was to acquire more fundamental knowledge on this behaviour in order to apply it to the area of driver modelling. The experiment was conducted with two vehicles on a motorway: a lead car and an instrumented vehicle driven by the subjects. In car-following runs, both cars drove at a predetermined speed and moderate speed increase or decrease manoeuvres were carried out. The second part consisted of approach manoeuvres: driving at a constant speed, subjects approached the lead car that drove at a lower, also constant speed. Hence, the subjects had to reduce their speed and then continue to follow the lead car. Both the subject's initial speed and the lead car's speed were varied experimentally. The results showed that steady-state car-following distance increased as a function of speed, but time headway did not. A constant time headway model can serve as a good first-order approximation of steady-state car-following behaviour, especially in a limited range of speeds. However, when covering the full relevant speed range (from standstill to motorway speeds), a more refined model seems more appropriate. In approach manoeuvres, the minimum Time-To-Collision (TTC min) was found to vary not only with absolute speed but also with relative speed. A driver-vehicle model that is based on simultaneous control of distance and relative speed showed similar behaviour as the subjects in the experiment in terms of acceleration and TTC. This shows that for the current manoeuvres (approaches with normal braking, with the driver fully prepared), TTC does not have to be included explicitly as a control variable in a driver model. See also C 9820 (ITRD 898630) and C 19242 (ITRD E206468).
Abstract