Walker proposes that there are three main factors shared between the successful ones: age of the city (older cities have a higher percentage of carless), and dominant universities.
Walker writes, "Most cities on this list display two or more of these factors, but a few are models for just one of them. San Francisco on the list because of age -- a rare western city largely laid out before the car-dominated era, and thus by far the densest big city in the west. Berkeley is there because it's small city dominated by a big university. And many cities are there because of relative poverty, including most of the cities that would be on everyone's list of America's toughest urban reinvention challenges."