[supertrope]

Here's a map of the US. https://i.redd.it/2nt3antutz8f1.png Green zones are counties with more than 10% of people commuting by transit.

It's essentially just NYC, Washington DC, Chicago, Boston, Philadelphia, San Francisco. NYC is 80% of USA public transit usage!

[OkayPhysicist]

Apparently there's a bus enthusiast in northern Nevada. (I'm guessing the real answer is towns small enough people walk to work)