If you look at the cities built in the Soviet times, where there were no parking space mandates, you'll see what will happen. People still buy cars, and those cars are just parked everywhere on the street, in the building courtyards, etc. Only on the last couple of decades (if that) underground parking became norm for high rise residential and commercial buildings in big cities. So unless you somehow plan on dissuading people from car ownership, I feel this will turn ugly... Especially in such a car-centric society like the US.