You're not referring to a specific problem here, and general size isn't an issue.

The comment you replied to is a bit shortsighted, public transit in more rural areas or small towns wouldn't work that well.

There's absolutely room for great public transit anywhere else though, cities and more sizable towns can easily have great public transport and there's even options for American suburbs. Trains connecting cities together in a lot of areas would also be relatively cheap for most places, and a lot of bigger cities used to have public transport that was eventually torn down to make room for cars.

I think a lot of you forget that things don't have to be perfect, especially first try and that things can easily be changed.