There's aren't that many cities in the US where significant banning of cars would be an easy endeavor, but there are plenty of places where reclaiming *some* streets from them would be trivial and cause little harm except "but my free on street parking."
If you visit old parts of European cities that didn't get bombed to bits, there are streets that are largely not compatible with automobile traffic. Cars aren't even always banned in these places, but nobody wants to drive down them unless they absolutely have to (or made a wrong turn). They're small, windy, dominated by pedestrians, have no on street parking, and just aren't useful places to drive. Sometimes cars are banned, or bollard systems exist to only allow local and otherwise authorized vehicles, but taking some streets away from cars doesn't even require banning them, just making them a bit more hostile to them.
US cities doesn't have many places like this, so it would require a conscious decision to make them car unfriendly. And who knows maybe I am dumb and this is a bad idea and even I don't think it's a good idea everywhere, but it's also a pretty easily reversible decision some places. Give it a try!
