Ironman reviews public transport architecture and notes:
First of all, to really make public transportation really work, you need to make everybody live and work within easy access of it. From the public transportation standpoint, where today’s cities go astray is in their grid system. Once city streets extend beyond easy walking distance of a main street or transportation corridor, public transportation begins to become more difficult to provide. As the distance grows greater, public transportation service becomes more and more difficult to provide, and as a result, it becomes more costly, less efficient and less effective as a viable means of moving people from place to place.
So, to make public transportation viable as the primary means of transport for an entire city, cities themselves need to be designed to closely follow a single transportation corridor.
He doesn’t actually talk about Manhattan, but if you live there, you know he is making a really good point.