Knowledge on the factors influencing driver speed-behaviour, the relationship between speed and traffic safety and means to influence speed behaviour is systematised. Expert judgements and the high proportion of injury accidents show that improved speed adaptation has the largest safety potential in the following situations: (1) Road surface, visibility and weather affected situations (e.g. slippery road, fog, darkness; (2) Places where sudden speed reduction is needed (e.g. motorway exits, sharp bends); and (3) Encounters with crossing-course both between motor vehicles and between motor vehicles and pedestrians/cyclists (e.g. at intersections, at zebra crossings). A study on driver speed behaviour in encounters with pedestrians at a zebra crossing shows that in such situations there is a need for better speed adaptation. In an encounter with a pedestrian, the driver has to be influenced before he reaches the "decision zone" at 50 to 40 m before the zebra crossing, in order to prevent the "signalling by speed" behaviour. A nationwide survey among 1000 holders of Swedish driving licences shows that the majority of the respondents are positive to a device which automatically lowers the maximum possible speed of the car in slippery conditions and poor visibility, as well as to a device which warns the driver or reduces the speed automatically if the car is about to collide with another road-user. A general system which prevents exceeding the prevailing speed limit is accepted by one third. A system, which limits the maximal speed of the vehicle in the actual situation via an in-vehicle equipment is proposed. A system algorithm to calculate the appropriate highest speed in different conditions is presented. The estimated safety effect of the proposed system, if all cars are equipped, is a 20%-40% reduction of injury accidents reported to the police. (A)
Abstract