Transit Access, but at What Cost? Affordability Outcomes Across California’s Transit-Oriented Development Typologies

As California continues to expand its investment in high-quality transit infrastructure, the need to align transit access with housing affordability has become increasingly urgent. In this study, we develop a replicable framework for classifying and evaluating over 60,000 high-quality transit station areas based on built environment characteristics and affordability outcomes. Using a 1.5-mi network-based pedestrian buffer, we apply K -means clustering to categorize station areas into four typologies: transit-oriented development (TOD), transit-supportive development, limited TOD, and transit-adjacent development (TAD). We then assess affordability using housing and transportation cost burdens across income levels, availability of income-restricted units, and statistical models, including random forest and Pearson correlation analysis. Results reveal that only 14% of station areas meet the criteria for full TOD, while TADs, comprising over 25%, exhibit the highest cost burdens and the lowest levels of affordable housing. Strong inverse correlations between TOD scores and affordability burdens indicate that transit-oriented urban form is closely linked to household cost efficiency. This framework offers a valuable decision-support tool for aligning land use, housing, and transportation policies to target resources where transit access and affordability are most misaligned.