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

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".