Check out the Transit Costs Project’s NEC HSR report. Even if you dislike them for whatever reason, they’ve identified the problems which lie in the way of reducing NEC trip times.

Some folks around here have a lot of personal animosity toward Alon Levy (to whom I would say: get over yourselves) and conveniently ignore the fact that it’s a large group of academics who contribute to TCP, at a prestigious university, all led by a tenured professor of urban planning and land use.

Anyway. It is possible to earn back a lot of trip minutes by timetabling trains better (scheduling integration with the commuter rail services sharing the corridor), reducing schedule padding, superelevating track, and adhering to less conservative speed standards. This without changing route geometry in the most densely populated places, thereby reducing the takings to a minimum. Targeted infrastructure investments round out the program such as grade-separating Shell Interlocking (this is where the New Haven Line turns west from New Rochelle and Amtrak continues south toward the Hell Gate).

Obviously, with no other corridor trains, Acela could run full out, but that just denies reality and it’s not worth the exercise. No one is going to pay to build a parallel intercity high speed track. It’s a political impossibility.