This post mainly responds to an argument made by Jim in comments that the core portion of the Northeast Corridor is New York-Washington, and New York-Boston is more expensive and less useful.
The Northeast Corridor has two halves: New York-Philadelphia-Washington and New York-Boston. The southern half is the more important one: according to PDF-page 41 of the Master Plan it carries 70% of the traffic, and the top city pairs are New York-Washington and New York-Philadelphia, both substantially larger than New York-Boston. Although the corridor is always treated as a single line, it is worth checking the value of upgrades separately, especially because the southern half is straighter and would take less investment to bring up to full high-speed rail standards.
However, even with such a disaggregation, New York-Boston is a valuable route, with more potential benefits than any other in the US except New York-Washington. For a first filter, we can look at city populations. New York’s size is such that even much smaller cities can be fruitfully connected to it by greenfield HSR. Seoul, of comparable size to New York, is connected to Busan, which is slightly smaller than Boston and slightly farther apart from Seoul than Boston is from New York; the intermediate cities, Daejeon and Daegu, are somewhat larger than New Haven and Providence. Total ridership on the Seoul-Busan segment of the KTX is about 30 million per year, and Korail appears to be making profits on the line, despite very high construction costs coming from heavy tunneling (about 40% of the route).
The first filter alone warrants further investigation of the route, even independently of New York-Washington. The costs of New York-Boston, while higher than those of New York-Washington, are not very high. We can put much of the New Haven Line in the “too hard” basket initially, but instead focus on high speeds between New York and Stamford and between New Haven and Boston and somewhat higher speeds between Stamford and New Haven than today. The average speed that can be squeezed with such investment is comparable to that of the KTX today, before the high-speed segments through two intermediate cities have been completed; those segments can then be compared to tackling Stamford-New Haven.
Of course, while adequate, is still nowhere nearly as good as what can be done on New York-Washington. It’s not just that this segment connects New York to two different cities the size of Greater Boston. Although today New York-Philadelphia has higher ridership than New York-Boston, this may well be reversed in the presence of full-fat HSR, since cutting a 1:05 trip to 0:38 does not provide the same competitive boost as cutting a 3:30 trip to 2:00, and Amtrak’s primary competition is highways rather than planes.
Rather, the benefits of New York-Washington are more in the distribution of the secondary centers. The biggest satellite metro area of Washington is Baltimore, on the line. Of Boston’s satellite metro areas – Providence, Worcester, and Nashua-Manchester – at most one can be served by any semi-reasonable HSR alignment. Philadelphia-Washington provides an additional market to be served. Washington’s population growth is much faster than that of the rest of the Northeast, and is comparable to that of the Sunbelt.
At the same time, there are benefits to building both lines; since under a phased program that built one first and then the other New York-Washington would be first, those benefits should be counted as benefits of New York-Boston. The biggest one is service through New York. Boston-Washington is a major air market: the O&D passenger volume between the Boston and Washington areas is 3.1 million a year; this is more than Boston-New York and New York-Washington combined, and Boston-Washington is both Boston and Washington’s busiest air city pair. In general, Boston-Washington and Boston-Philadelphia are located at more favorable ranges for HSR’s competitiveness than New York-Boston and New York-Washington, on which the trip time advantage versus cars and buses is smaller.
If we take Boston-Philadelphia and Boston-Washington and slightly more than double the size of today’s air market – the same ratio of present-day HSR traffic to pre-HSR air traffic between London and Paris – we get an additional 9 million passengers a year, small compared to the possibilities of the other city pairs but non-negligible.
The other issue is rolling stock and operating plan. Because the Northeast Corridor runs as one route, and there is no point in separating its two halves operationally, the same rolling stock that runs south of New York also has to run north of New York. In particular, we obtain the following situation:
– Traffic purely south of New York justifies rolling stock that could in principle achieve much higher speeds north of New York.
– Because of certain capacity problems, both real and imagined, a few strategic bypasses and (near Boston) commuter rail modernization can have outsized intercity trip time benefit relative to the cost. A high-speed train that gets stuck behind commuter trains pulled by diesel locomotives does Boston-Providence in about 35 minutes. One that shares tracks with punctual modern EMUs can do the same in 20.
– At low levels of infrastructure investment, the cost of new rolling stock can be sizable compared to the cost of infrastructure. Half-hourly service with 16-car trains, one possible initial service plan, costs $250 million times the one-way Boston-Washington trip time in hours including turnaround time, plus spare ratio. 15-minute service requires double that cost, naturally. None of the New York-Boston projects, not even “buy the MBTA better trains,” flips to negative cost this way, but some have lower cost as a result.
– Shared-track HSR requires very good punctuality. Coming south from Boston, trains have no reason to be off-schedule in New York – Metro-North is reasonably punctual (though not enough for HSR) and both between the Rhode Island/Massachusetts state line and New Haven and between New Rochelle and New York Amtrak owns the tracks and runs the most trains – but the bypass and junction separation will help further. Coming north from Virginia there are much bigger problems, but trains can dwell arbitrarily long in Washington for schedule buffer, which they can’t in New York.
What this means is that it’s best to phase Northeast HSR investment throughout the entire corridor. New York-Washington should have the priority because it’s cheaper and has more traffic potential, but unless for some reason there is no money (not even about $4 billion for immediate improvements plus a little more for a bypass), parts of New York-Boston should be in the first phase.
Arguably, even true branches, such as to the Keystone Corridor and Springfield, can get through-service early. Those do not have the ridership potential of the core route, but electrifying New Haven-Springfield to run trains through, and programming extra trains for Keystone, can be done within a few years. The limit perhaps is only rolling stock, or more precisely what to do with the electric locomotives that would become obsolete (they already are, but are a sunk cost, and buying new HSR trainsets now becomes an additional one-time cost).