People are concentrating too much on transportation methods in this discussion. Start with the development pattern. Cities can change their zoning codes to allow for more construction - housing, office space, retail, etc. Doesn't have to go from 2 stories to mega scrapers, you just need a good healthy mix of 3 to 5 story buildings with not an excessive amount of parking. Change the zoning laws, and you'll see a development pattern more conducive to pedestrians, bus transport, bikes. That's when you can start arguing for reducing car usage.
For cities with healthy CBDs, they can already go this route of pedestrianizing but the rest of America, it's too sprawled but you can start with filling in places with more housing considering the need. Once you get enough people, frequent bus routes might make sense or bike paths. Maybe some road diets. It's going to be a gradual change for those willing to change. There's also going to be a lot of places that won't change and if we stop subsidizing road construction and the sprawled environment, they'll change on their own or will just fail. There's simply too much car oriented crap to make everything work in the long run.
For cities with healthy CBDs, they can already go this route of pedestrianizing but the rest of America, it's too sprawled but you can start with filling in places with more housing considering the need. Once you get enough people, frequent bus routes might make sense or bike paths. Maybe some road diets. It's going to be a gradual change for those willing to change. There's also going to be a lot of places that won't change and if we stop subsidizing road construction and the sprawled environment, they'll change on their own or will just fail. There's simply too much car oriented crap to make everything work in the long run.