That seems to be happening, at least in some European cities. Paris for instance is (very) slowly chasing cars outside of the city. London has the congestion tax. The problem of course is that you need the infrastructure to replace all the cars and public transportation in Paris is close to saturated. Still, it's probably a move in the right direction IMO.
Sometimes it really is a zero-sum game. Pedestrians, bikers, personal cars, buses and trams compete for the same surface area, and out of those cars are the main cause of congestion due to their abysmal people/m^2 value.
