Yeah, imagine "all" those 8 or 9 million registered Democrats in California wanting to get rid of their cars, esp when so many have no way to get to work without their own "wheels".
As an environmentalist, I am very pro public transport, but it has to actually exist and function properly.
First thing I would do is make it very expensive to take your car into the heart of the city, and then provide a stream of "people-movers" (shuttle buses) to transport those who are happy for that option.