The surveying of travel behavior changes toward more sustainable mobility practices raises many methodological questions. First is the choice of method, determining how to analyze these behavioral changes via their contextual, temporal, and multifactor dynamics, while attempting to control possible biases. This paper proposes an examination of the use of qualitative methods through two empirical research projects and finds that the order and content of the interview protocol questions can potentially bias the responses. This behavior can be observed specifically with respect to the weight of the dominant social norm (the phenomenon of "social desirability") and the production of justifications when discrepancies appear between practices described and stated environmental beliefs. One particularity of the qualitative method, reinterviewing the subjects, provides many advantages for analyzing both the process of change and the effects of the interview. Indeed, the interview itself may play a part in modifying subjects' attitudes and behaviors: it can provoke changes in individuals' responses and can modify their attitudes toward a topic, causing them to think about the interview. In fact, the interview itself can transmit information and thus encourage a change of practices. Finally, the results are discussed with reference to experimental programs for voluntary travel behavior change.