Abstract : This thesis considers the problem of modal shift in terms of the limitations that exist in the classical model designed for understand transport mode choices. Three major dimensions that address individual behaviour are studied by means of three studies with residents of the Paris region in France. The naives explanations of modal choices for 307 participants are used in the first study to consider the determinants of their various transport preferences. The results show that from the point of view of these users, choices are primarily based on the instrumental characteristics of the transport modes. Additionally, analyses of the determinants of different transport mode choices show that the individual preference for minimising commute time does not distinguish car users from users of public urban rail transport. Study 2 considers the relative importance of symbolic parameters by manipulation of two hypothetical decision-making contexts for 200 participants. The results show that an instrumental parameter (commute time) and a symbolic parameter (social mix) have a similar impact on modal choices. Study 3 addresses the need to consider the cognitive dimensions of the transport mode decision, by manipulation of the attention given by 438 individuals to the evaluation of their freedom of choice. The results show that the feeling of freedom of choice tends to be less dominant in central processing than in peripheral processing. Together these studies show some effects of socio-demographic variables. The whole thesis emphasizes the need to take into consideration the behaviour of the individuals in order to increase the efficiency of strategies promoting the modal shift.