My research, supported by the Dutch Ministry of Traffic and Waterways, was among the first to recognize that the decision between different modes of transport can be framed as a social dilemma , a conflict between private and public interests. My research showed that there are systematic personality differences underlying transport mode preferences. How difficult it is to change travel mode decisions was demonstrated in evaluation research we carried out in the Netherlands on the effects of a field-experiment,, the carpool lane (Van Vugt, Van Lange, Meertens, & Joireman, 1996). We have also carried out comparative studies in the UK and US (Seattle) to determine public support for government plans to reduce car use.