I don’t think a car-free city actually exists. The article mentions Copenhagen:
“[London] has avoided the kind of outright car bans seen elsewhere in Europe, such as in Copenhagen”
I’ve been to Copenhagen. There are cars throughout the city. There are some cycle-only paths that connect to intersections with cars. I cycled along side cars all over the city. Apparently Wired is calling car-reduced cities and cities with small car-free regions a “car-free city”.
Exceptionally, Brussels is a car-free city but for only one day out of the year. And car-free day falls on a Sunday. On that day it becomes illegal to drive a car in the city center without a special pass after showing you have good reason to use a car on that day. But even on that day, the outer region of Brussels is unaffected.