Inappropriate high speed: who does it and why?

Ways of defining inappropriate high speed are discussed. High speed leading to loss of control of a vehicle and a collision is self evident. In other cases, driver retain control of vehicles but are driving too close to the threshold where the demand of the driving task may exceed capability. This is usually considered reckless or dangerous driving. Alternatively driving at high speed can be defined in terms of violation of traffic law. However, depending on the driving conditions, an inappropriately high speed may be lower than the legal speed limit. Highway design is an important consideration in drivers' choice of speed. The likelihood of collision involvement is increased for drivers adopting a different (higher) speed from that of other drivers using the same highway. The attitudes and behaviour of high risk threshold drivers, low risk threshold drivers, opportunistic drivers and reactive drivers are compared. Young, male and inexperienced drivers were most likely to have a high risk threshold. These drivers tended to move into safer behaviour groups with age and experience. For the covering abstract see ITRD E138063.