They are in most European cities anyway. I'm in a - for the US small, for Europe mid sized city with a pop of roughly 400k. City center is banned to cars. You're supposed to park on the outskirts or take public transport into the center. (Or bicycle).

The result is that almost no one goes there anymore. All the inner city shops are closing down - while the mall style shopping centers on the outskirts are flourishing.

Walkable cities sound great in theory. Until you realize that shopping groceries _really_ sucks when you have to carry full bags for 3 kilometers or have to use over-filled public transport.