This is a dream. In places where public transportation is not "underdeveloped" it's still often slower and less convenient.
In the Bay Area, if the government wanted to do something about the environmental damage caused by cars, they'd get rid of the tolls on the bridges. Adding more BART service (which you'd need, since it already runs at peak capacity during rush hour -- and you probably couldn't get due to equipment shortfalls) wouldn't fix the fact that it takes forever to get places ... because it's far!
/jordan