Audience effects on individual behaviour have often been interpreted in terms of increased arousal, which in turn enhances the emission of dominant responses. However, such drive-based explanations do not readily fit all of the evidence on audience effects. The present study examined the influence on driver behaviour of the presence of a passenger. Solo drivers or drivers with one passenger were covertly followed and observed as they drove along a major urban road on which a 30 mile an hour speed limit applied. The sex of both drivers and passengers was noted, and they were classified as 'younger' or 'older' depending on whether they appeared to the two members of the research team to be under or over 30. The target cars were followed for about 4 minutes during which time the researchers noted any actions by the driver of the target car which they considered to be illegal, discourteous, or a breach of the highway code. The main findings were that the incidence of both signalling and speeding appeared to be reduced by the presence of certain types of passenger. These results seem to support a control theory rather than a drive-based account of social facilitation. In addition, the incidence of close following and speeding differed significantly across type of driver. Taken together, these results suggest ways for improving road safety propaganda based on the specific norms salient for specific categories of road user. (TRRL)