San Francisco's many single-family-home neighborhoods have all you really need to accomodate car storage: garages instead of living space on the ground floor. Houses still come right up the sidewalk and squeeze wall-to-wall against each other.

Typical American suburbia takes density way lower than that. People here seem to value that separation for reasons above and beyond their parking needs. For example, not hearing the neighbors' footsteps through the ceilings or their TVs and family disputes through the walls. Giving each child their own bedroom. Having room for play and gatherings in the backyard. This suggests that, even without cars, we'd still insist on a pretty low densities. (Since it is homeowners in the center who control land use in the center, the frustrations of outer-ring commuters under such an arrangement don't make a difference).

I'm fortunate that I can afford to live in a high-rise district and commute in reasonable time by train and elevator. But even with so many places a short walk from home, it's a big metro area - there are many more I want to go which are not so close. Without a car, I felt isolated and trapped. It's great to have neighborhood businesses, but you get tired of the monotony after a while.