No one is going to bike 15 miles for a dozen eggs, and no one is going to build a supermarket closer than that, and I'm nowhere near an extreme case. It will take more than a century to restructure the US away from individual vehicles, if it's done at an insanely fast pace.

Public transport relies on the value of having a public around the stops, or the ability to concentrate the public in crossroad areas. It's already too late for that in the US, and will take multiple generations of land transfer to fix it. The entire country was literally built on expansionism and isolationism. Fixing our cities is the easy part, and that alone will take more than all government expenditure ever, over half a century at the least. And that's assuming we don't go bankrupt simply supporting the retiring population we have right now, let alone additional expenditures.