In Japan, they are developing underground train stations the trains are traveling 300 mph and more.  To replace all the tracks and make all the trains fast and efficient it will cost 55 billion dollars. I think that this will be a nice way for transportation since there isn't enough room for buses and trains and large transportation vehicles. Japan should work with the money they have building a little at a time and eventually this cities will be transformed to using bullet trains. If this works well in Japan other countries will most likely catch on and use their idea for these trains.