CHOICE OF TIME-HEADWAY IN CAR-FOLLOWING AND THE ROLE OF TIME-TO-COLLISION INFORMATION IN BRAKING

Time-headway (THW) during car-following and braking response were stud ied in a driving simulator from the perspective that behaviour on the manoeuvring level (e.g. choice of THW) may be linked to operational co mpetence of vehicle control (e.g. braking) via a process of adaptation . Time-headway was consistent within drivers and constant over a range of speeds. Since time-headway represents the time available to the dr iver to reach the same level of deceleration as the lead vehicle in ca se it brakes, it was studied whether choice of time-headway was relate d to skills underlying braking performance. The initiation and control of braking were both affected by time-to-collision (TTC) at the momen t the lead vehicle started to brake. This strongly supported the idea that time-to-collision information is used for judging the moment to s tart braking and in the control of braking. No evidence was found that short followers differ from long followers in the ability to accurate ly perceive TTC. There was, however, evidence that short followers are better able to programme the intensity of braking to required levels. Also, short followers tuned the control of braking better to the deve lopment of criticality in time during the braking process. It was conc luded that short followers may differ from long followers in programmi ng and execution of the braking response.