Having looked into why high-speed rail from New York to Boston should go through Providence, I want to explain why it should go through New Haven, rather than through any of the fanciful Long Island routings proposed most prominently by the Penn design group. Like Hartford, Long Island should have high-speed trains use the LIRR Main Line, but at medium speed rather than high speed, and with careful consideration to the much more important needs of commuter rail.
Although the LIRR Main Line shares one characteristic with the New Haven-Springfield line, namely that it is very good for 160-200 km/h but bad for 300, the reasons are subtler and less geometric. The most visible is NIMBYism. Even increasing the traffic of existing LIRR trains raised the ire of some suburbs along the Main Line, which opposed the three-tracking project (since canceled due to budget shortfall) on the grounds that extra train traffic would reduce quality of life and that eminent domain would be required. This is not Caltrain, whose local residents do not know what electric trains sound like; this is Long Island, which has lived with these trains for generations. Introducing HSR is asking for trouble.
Of course, the same could be said about any suburb that HSR needs to pass through. Connecticut is full of NIMBYs, just like Long Island. The reasons usually given for avoiding the existing Shore Line are that it’s too developed and has too much local opposition. But those are present on Long Island, and are worse because of the higher population density. For examples, compare Westport and Cos Cob with Brentwood and Farmingdale. The LIRR offers multiple straight rights-of-way, but all are going to have the same speed limits as heavily upgraded and modified tracks on the Shore Line – 250 km/h in the better parts, and 200 in the worse parts.
The Penn design proposal is not even the best Long Island proposal, for three reasons:
1. It insists on proceeding from Penn Station to Jamaica on the Lower Montauk Line. If a connection from the line to Penn Station opens, it’ll be far more useful for local rail, while intercity rail can use the Main Line. The difference between appropriating a Manhattan-accessible Lower Montauk Line for HSR and replacing the Lexington Avenue Line with a truck tunnel is one of degree, not kind; in both cases, local passenger rail is the most valuable use of the infrastructure.
2. It departs from the Main Line to use the Hempstead Branch (necessarily eviscerating commuter service) as well as abandoned tracks through endless residential suburbs, full of urban grade crossings. The Main Line has grade crossings and would need to be four-tracked, but the local NIMBYs actually supported grade separation, and multi-tracking at least could be sold as the local transit improvement project that it is.
3. Last and worst, it sharply veers north after stopping at Ronkonkoma, along a curve whose radius judging by the alignment map is around 900 meters (=150 km/h if superelevation and cant deficiency are set at normal HSR levels, or 170 km/h at cutting-edge levels). Then it crosses the Long Island Sound at its widest, so that it adds more than 20 kilometers to the New York-New Haven route length over the Shore Line, all at medium speed.
A route similar to the Penn design route but using the more feasible Main Line alignment would be 9 minutes slower than the optimal Shore Line route – 41 versus 32 minutes – with stops at Jamaica and Hicksville, enforced by unfixable track curvature near the stations. But in addition to the extra travel time, fixing the alignment through New Rochelle, Darien, and Bridgeport is far cheaper than a long undersea tunnel. A better Long Island route would follow the Main Line to the end and tunnel near Greenport, trading deeper waters for shorter tunneling and a route length comparable to that of the optimal Shore/I-95 alignment, so it could achieve a comparable trip time. But even that’s unneeded: it’s 15 km of deep tunneling, whereas if one is willing to slightly compromise on trip times, the only Connecticut tunneling required for a Shore Line fix is 3 km in Bridgeport.
The other problem is what to do about commuter service. The Providence Line’s traffic level is low enough and its average interstation is long, allowing a blended plan. Shared tracks between New Rochelle and Penn Station would see more commuter traffic, but intercity trains would go slower anyway, and there is more room for four-tracking. The Ronkonkoma Branch’s 10-minute peak service requires at least one overtake between Hicksville and Ronkonkoma and probably two, in addition to four-tracking the Main Line; this is feasible, but less than optimal, and the overtakes would have to be constructed in more constrained locations than those available on the Providence Line. East of Ronkonkoma commuter service may need to be cut, but this is less of a problem on account of its low traffic. On the other hand, the Main Line west of Hicksville is not a problem with four tracks, and neither is the New Haven Line – express commuter trains could weave in and out.
On the benefits side, offering Long Island service to Boston that doesn’t go through New York is better than not doing so. However, the difference in benefits with New Haven, while positive, is smaller than it seems. The New Haven Line has almost as much ridership as the LIRR Main Line, and Stamford is a bigger edge city than Mineola and Garden City. On top of that, since the optimal LIRR option connects to the Shore Line in the far east of Connecticut, there is no hope for service to Hartford except on legacy track. On balance, the advantage of the LIRR option is just service to Jamaica, a larger draw than those smaller cities and suburbs, but there the time saving is the smallest.
On top of that, does such a small benefit really justify the cost? Having some high-speed trains run through to Jamaica, Mineola, Hicksville, and Ronkonkoma at lower speed requires re-electrifying the LIRR with catenary, which is a fraction of the cost of all those urban grade separations and 1-2 order of magnitude cheaper than an undersea tunnel and land connections. On a similar note, since half an undersea tunnel is of no use, it’s harder to break construction into small chunks if it is necessary, putting it at a disadvantage against a route consisting of cutoffs and modifications of the existing line. The route of 1834 may work now that we can build tunnels, but the cost structure favors that of 1846 and 1852.