[MereInterest]

Such a chart would in no manner prove your point. Something can become prevalent could be because (a) it is the preferred option out of many equivalent and equally available options or (b) it is the chosen option due to having been given preferentially treatment. Given that your time period contains Eisenhower's expansion of the federal highway system, option (b) is the more reasonable interpretation.

[momokoko]

We've seen the phenomenon globally.

[coldtea]

Not in the way it is in the US...

Even Paris discussed in TFA is 10 times better than 99% of American cities... and most of European cities are even better walkability wise...