California's SB 375 law, which is meant to "reduce greenhouse gas emissions by lowering vehicle miles traveled," failed in San Diego because the city government dropped the ball:
"But at the macro level, (San Diego Association of Governments') draft plan simply doesn't take any aggressive steps to change the status quo. For example, SANDAG doesn't consider front-loading transit plans over highway projects as a possible solution to sprawl, and the agency doesn't appear to encourage aggressive local government policies to plan for more infill development. Instead, SANDAG appears to have taken a passive role, largely compiling existing local land use plans and forecasting based on them."
"All along, SB 375 supporters appeared to be counting on the goodwill of the basically toothless regional entities to be forward-thinking and push their local governments to change, either through incentives or by getting people excited about a more compact development footprint."