Travellers commit themselves to particular behaviours through the ownership of cars and season tickets. They trade a large one-off payment for low or zero marginal cost at the point of use. It can be assumed that these commitments influence travel behaviour and future commitment situations. To the knowledge of the authors there is no literature which addresses the choice between the commitment to the one or the other mode and its impacts on travel behaviour as well as the temporal dimension. The paper presents models using structural equation modelling to test a-priori hypotheses on the paths linking car-availability, season-ticket-ownership and modal usage at three different time periods. Modal usage is operationalised as the number of trips by car respectively public transport. The models are based on two different panel surveys (Germany and the Netherlands). The results show that there is high stability in car-ownership and a relatively high stability in season-ticket-ownership (only for Germany). The commitments influence modal usage whereby the influence on the respective mode is higher than the influence on the other mode. The relationship between the two modes is a substitutive one.