I live in Tokyo: there's over 40 million people in the greater metro area. It's the largest metro area in the world. There's hundreds of train/subway stations and most of the population gets around by public transit, along with cycling and walking.
Population size isn't the problem, the problem is the way American cities were built. If you want public transit to work, you have to make cars extremely inconvenient, which means little or no parking (and the parking that exists is very expensive), high density, and zoning that allows all this.
Population size isn't the problem, the problem is the way American cities were built. If you want public transit to work, you have to make cars extremely inconvenient, which means little or no parking (and the parking that exists is very expensive), high density, and zoning that allows all this.