Are there safe and unsafe drivers?

One of the aims of most driver screening practices, in addition to a variety of possible diagnostic and rehabilitation activities, is to exclude from the driver population those persons who are not "safe enough" to drive. In order to realise this aim, i.e., to decide whether or not somebody is "safe enough" to drive a car, we must estimate his or her individual risk as driver and compare this risk level with a threshold value. In the present paper, we claim that estimation of individual driver risk for screening purposes implicitly relies on the following assumptions: (1) there is such a thing as individual driver risk; (2) it can be expressed as one parameter; (3) it can be measured or estimated; and (4) thresholds dividing the driver population into safe and unsafe can be identified. The theoretical and methodological problems presented by these assumptions are critically discussed. (c) 2006 Elsevier Ltd. All rights reserved.