North American (and to an extent Australian) cities were built with the automobile in mind, it’s not a surprise as they were growing during the auto age. Most older world cities were built when the main form of transportation were horses, carts, bicycles or legs. Most North American cities have enormous sprawls and having a subway system with a decentralized population is not efficient or cost effective. Unless Americans are willing to give up (or more likely can no longer afford) 2500 two car garage houses and willing to move into condos and other high density housing, a subway system just doesn’t make any financial sense.