That's true, but whether banning cars or making it less attractive to cars (e.g. with London's congestion charge), the point is that places already have people working on road planning/etc., it can be done with humans making decisions, not a piece of code going "if (congested) {ban cars} else {allow cars}".

To use Oxford as a small example of more than a toll, there's a few roads in the city centre that only buses/taxis are allowed to use, and a few roads that only pedestrians can use (with some time-specific exceptions for loading/unloading/etc.). Nobody looks at it and thinks "well now it's not congested we should allow cars again".