The success of campaigns and policies directed towards reducing private car use is, for the most part, dependent upon understanding the psychological factors that influence an individual's travel mode decisions. In general, however, interventions to reduce car use have been based on informal conceptualisations, designed without elicitation research, and directed primarily at providing information about the negative consequences of car use. This information is usually not sufficient to change behaviour. In fact, whether people choose to drive or take public transport has been found to be only weakly related to their knowledge about the environmentally damaging effects of extensive private car use. Intervention strategies based on empirically validated theories are more promising, though in relation to the choice of travel mode, there is a lack of research that utilise such approaches.