This paper explores how the quality of the pedestrian environment around transit stops relates with transit ridership. The primary hypothesis tested is that transit tripmaking is higher in urban environments that are more conducive to non-motorized travel, given that bus transit systems are most frequently accessed via walking or biking. A secondary goal is to contribute to an improved understanding of the measurement of the built environment in geographic information systems (GIS). A composite measure of walkability—incorporating land use mix, density and street patterns—was developed for all transit stops in San Diego’s Metropolitan Transit Systems service area and used as a measure of the built environment. Findings indicate a small but significant, positive relationship between the walkability of the built environment and transit ridership.