Support for transportation policies and investments is increasingly shaped by partisan ideals. Less well documented is the role of partisanship relative to potential mediating factors like transportation-related values, beliefs about the possibility of change, self-interest, and knowledge. We surveyed a representative sample of 600 U.S. adults about these factors, their political ideology, and their willingness to change the automobile-oriented transportation status quo. We found considerable support for change but also deep partisan divides. In exploring the pathways between partisanship and policy preferences, we found that values and beliefs about change are both deeply partisan and closely associated with policy preferences. By contrast, the results were mixed for self-interest and transportation-related knowledge. Ultimately, we found that these four pathways explain much, but not all, of the partisanship in transportation policy preferences. Very conservative respondents opposed reform efforts above and beyond what we would expect from their values, beliefs, self-interest, and knowledge, indicating continuing salience of partisanship. Our results suggest that transportation reforms enjoy broad public support in urban areas with moderate and left-leaning populaces but may struggle to win approval at the regional, state, or federal level due to partisan geographic sorting. Some planners, policymakers, and advocates may choose to embrace partisanship, but doing so may exacerbate tensions and hamper progress. Others may prefer to tackle the pathways between partisanship and preferences without deepening partisan divides. For instance, practitioners may seek to increase support for reform by tackling widespread misunderstandings about induced demand or by installing pilot projects to help the public understand that it is possible to quickly and inexpensively change infrastructure and travel. [ABSTRACT FROM AUTHOR]