I would suggest that saying anything as substantial as an automobile being "widespread" or "affordable" during the 20s and 30s is overreaching, considering there was something of a worldwide economic instability at the time.

I think a major piece of the puzzle is that living in a car dependent area has been an effective way for the middle class to segregate from poor people.

For me, personally, this very much drives my choice to live in the suburbs and to drive a car instead of using public transportation: I'm unwilling to settle for the lowest common denominator.