Recent statistics about the low level of participation by individuals in physical activities as well as a generalized propensity to use private vehicles have broadened the scope of transport studies to the sphere of health and well-being. The current shift in travel demand modeling to the activity-based paradigm is central to investigating which population segment is more likely to opt for environmentally friendly and energy-efficient vehicles, alternative modes of transport, and a rational use of the motor car. A mixed, joint Tobit-probit model analyzes the effects of time allocation for daily activity on the propensity to sustainable trips. The model is applied to a sample of workers and students age 14 and older, drawn from a time-use survey conducted in Turin, Italy, and its metropolitan area. The analysis suggests the presence of self-selection effects between active lifestyles and sustainable mandatory trips. The model predictions highlight the substantial contribution of transportation interventions in getting individuals to engage in healthier behaviors.