Abstract
A method of evaluating an automatic queue warning system is outlined. The main object of the evaluation is to measure the effect of such a system on traffic behaviour and road safety, although the overall journey time is also examined. The chosen method of research entails before- and after studies, if possible complemented with control groups. Factors likely to have a disturbing effect on this method of research are also discussed, together with their respective solutions. Finally, a look is taken at the number of accidents required for a statistically-reliable analysis.