I don't like cars, yet, I don't think there can be any general solution. How do you define "city center" for a start ? Where does it start ? In Berlin, for instance, the streets are very large and the city so widespread - besides there is no "city center" in Berlin. It would be quite inappropriate to ban all cars altogether.

Similarly, I wouldn't know what to answer for Paris : in a way the "city center" is everywhere, or there are many city centers.

I think you can start by charging a lot for car parking, as they do in Paris and in Berlin. Believe me, people will think twice before they use their car to go to the "city center". As a next step, maybe you can have a few single streets as "car free". It's not bad for the economy if it's a shopping street, on the contrary !

Whatever solution, it should be left to the individual town to decide.

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______________________Own only what you can always carry with you: know languages, know countries, know people. Let your memory be your travel bag.”___________________Alexander Solzhenitsyn