Today in California, urban infill development proliferates. A welcome alternative to decades of greenfield expansion, this infill boom is the culmination of regulatory incentives like SB 375, economic growth in urban areas, as well as increasing awareness of the climate evils of vehicle emissions (quantified in vehicle miles traveled, or VMT). The social, spatial, environmental, and economic effects of this infill boom are far-flung and implicate many areas of study. This Note focuses on the environmental health implications of siting infill development near increasingly trafficked transit corridors. By placing people in closer proximity to work and transit, infill development lowers VMT; however, this land-use pattern potentially exposes more people to fine particulate matter from vehicles. The California Air Resources Board and Air Quality Management Districts initially attempted to solve this exposure issue through the California Environmental Quality Act (CEQA). Concerns about the suitability of CEQA to address these “reverse” environmental issues, perceived barriers that CEQA poses to infill development, and environmental health collided in California Building Industries Association v. Bay Area Air Quality Management District. Though seemingly contrary to decades of planning practices in California, the California Supreme Court’s decision offers a new way forward—a path planners and health officials in San Francisco began in 2008—that could potentially make urban infill easier to develop as well as healthier for residents.