This paper considers valence-based framing, i.e. a description of equivalent outcomes in either a positive or negative light, in order to reduce transport-related CO emissions. This nudge is easier to implement than more traditional tools, such as taxation, and does not rely on the stringent assumption that individuals are fully rational. The findings from a discrete choice experiment focusing on long-distance travel choice are reported herein. Results indicate that a loss framing on CO emissions significantly increases the respondents’ pro-environmental behaviors. Moreover, it is shown that the magnitude of the framing effect depends on individuals’ motivational orientation, and that preferences are sensitive to individuals’ psychological factors (i.e. preference for the future and environmental self-identity).