There is little research on the role of motivations in predicting intentions to engage in pro-social or pro-environmental behaviours. In this article we rely on the Self-determination theory (SDT) to assess the relationship between individual motivations (autonomous and controlled) and intentions to modal shift. We additionally evaluate the mediating role of active mobility habits in this relationship. To do this we build and test theoretical models using structural equation modelling. The results show that if habits concerning the use of alternative modes to the car are not taken into account, the autonomous motivation has a significant impact on intention, but not controlled motivation. However, the introduction of habits in the model shows that they fully mediate the relationship between both motivations and intention. These results are useful for a better understanding of the psychological mechanisms of modal choice changes and the targeting of measures aimed at encouraging the use of active modes.