This particularly applies to the PHL-NYP segment, but the question can be extrapolated to other parts of the NEC. Even assuming a new set of tracks goes in parallel to the existing ones for the super-duper HSR plan, what is the per-hour track capacity of a set of four RR tracks? Particularly in terms of higher-speed trains, I'd think that the capacity becomes static at some point, if not potentially falling off (any gains in moving trains faster get offset by needing more spacing to allow a train to stop in an emergency).
The question arises because I ran some back of the envelope calculations for Amtrak's long-term projections if they get their fancy new 220 MPH alignment put in: According to their stats, the south-of-NYC and through-NYC traffic totals would come to just under 30,000 passengers per day (on average) on the Regional trains and another 30,000 the High Speed trains. Assuming 300 passengers per train on average (i.e. accounting for the fact that you can pack more folks into that 8:30 AM train than you'll get to sign onto the 9:00 PM one), you're rapidly closing in on 200 trains per day on a single alignment if the per-day average were to hold across every day...and more practically, probably closer to 250 trains per day on weekdays (but "only" 150-175 on weekends). Note, by the way, that this does not count in Keystone service trains (which probably throw another 10-20 on top of that), nor does it account for any NJ Transit trains that would be getting thrown into the mix.
The Hudson tunnels aren't the big issue in my mind...you can juggle scheduling there a bit better, particularly since it's just one segment. What's setting up trouble is once you get further down the line...can a single alignment of some sort take the sort of rush hour peak traffic that these figures imply, or would Amtrak have to kick trains onto another alignment (further east or west) that "tags in" at Philadelphia? I ask about the south-of-NY traffic because Amtrak at least has some plans to split things north of NYP...but the southern end of things, in addition to having higher demand (albeit only marginally so under those projections), makes no plans to have a second alignment...which implies either some six-track behemoth or some other sort of rearrangement.
The question arises because I ran some back of the envelope calculations for Amtrak's long-term projections if they get their fancy new 220 MPH alignment put in: According to their stats, the south-of-NYC and through-NYC traffic totals would come to just under 30,000 passengers per day (on average) on the Regional trains and another 30,000 the High Speed trains. Assuming 300 passengers per train on average (i.e. accounting for the fact that you can pack more folks into that 8:30 AM train than you'll get to sign onto the 9:00 PM one), you're rapidly closing in on 200 trains per day on a single alignment if the per-day average were to hold across every day...and more practically, probably closer to 250 trains per day on weekdays (but "only" 150-175 on weekends). Note, by the way, that this does not count in Keystone service trains (which probably throw another 10-20 on top of that), nor does it account for any NJ Transit trains that would be getting thrown into the mix.
The Hudson tunnels aren't the big issue in my mind...you can juggle scheduling there a bit better, particularly since it's just one segment. What's setting up trouble is once you get further down the line...can a single alignment of some sort take the sort of rush hour peak traffic that these figures imply, or would Amtrak have to kick trains onto another alignment (further east or west) that "tags in" at Philadelphia? I ask about the south-of-NY traffic because Amtrak at least has some plans to split things north of NYP...but the southern end of things, in addition to having higher demand (albeit only marginally so under those projections), makes no plans to have a second alignment...which implies either some six-track behemoth or some other sort of rearrangement.