Suburbs and work commutes are what makes this seem unlikely right now. After WW2, cheap production of cars, then followed by the development of the Interstate highway system allowed people to move out of cities, which in turn allowed long distance commutes to jobs in the cities. Coincidently, that was about the last time many public transit systems had any major increases in either infrastructure spending or new lines (e.g. here in New York City) or saw reduction in services. Until gas prices get to a level where they encourage people to stop long distance commutes, nothing will really change in this country.