Anyone who's sat in Bay Area traffic wants changes -- don't let that cloud the facts: car based transportation is not a major source of emissions in the Bay Area, and overall emissions have been dropping since at least 1990 [1].

Particulate matter (PM10 and PM2.5, aka the stuff that causes disease) is less than 20% due to on-road vehicles. The big sources are "combustion" (burning organic matter) and fires. [1]

[1] http://www.baaqmd.gov/~/media/Files/Planning%20and%20Researc...