The percentage of people in the US that live in an area dense enough where even an ideally designed public transport system would match the convenience of a car

The percentage of people in the US that live in an area dense enough where even an ideally designed public transport system would match the convenience of a car is in the low single digits. When I go to European cities with these great public transportation systems everybody loves to talk about, what to I see on the road? Lots of cars. Cars aren't going anywhere.