An extended version of the theory of planned behavior (TPB; Ajzen, 1991) was used to explain travel mode choice. As a new predictor, perceived mobility necessities (PMNs) were introduced, which are defined as people's perceptions of mobility-related consequences of their personal living circumstances. The database consisted of a survey of 1,545 car users in 3 large German cities. Using structural equation modeling, PMNs were integrated into TPB and showed the expected significant negative effect on use of environmentally friendly modes. In-depth interviews with 82 selected participants indicated that PMN moderates the relationship between public transportation attitude and intention. This moderator effect was confirmed by a regression analysis. The extension of TPB by PMN allows deduction of more differentiated intervention strategies.