Even if you start designing new small cities to accommodate no automobiles, you will not be able to eliminate automobiles outside those cities, nor will you be able to force everyone to live in them.
You'd basically just be building a car-less retirement community and hope that young people opt into it.
Build light rail in existing cities, build parking lots for people who need to drive to a light rail station, and start charging a toll for people who drive in places where light rail could take them. Slowly but surely you can turn a city built around cars into a city built around public transit. This is possible in small and large cities and would reduce congestion, pollution, and the danger to pedestrians and cyclists.
You'd basically just be building a car-less retirement community and hope that young people opt into it.