Staten Islanders’ desire for a subway connection got me thinking again about my previous proposal for a tunnel from Staten Island to Manhattan, possibly with a cross-platform connection to Brooklyn and New Jersey. From all points of view, it is desirable to build a regional rail hub near Fulton Street, and connect it to nearby commuter lines, creating a second pole for an RER- or S-Bahn-like system in New York, in addition to a Midtown pole centered around Penn Station. My intention in this post is to discuss tradeoffs in choosing how to build it.

As the source of the ARC and ESA cost overruns is the station caverns in Manhattan, the Fulton Street station should be minimalistic: as close as possible to the surface (closer to 20 meters underground than to 55), without a full-length mezzanine, and with only four tracks, one to each of Midtown, Brooklyn, New Jersey, and Staten Island. It should under no circumstances look like the ESA extravaganza. This economizing means it’s difficult to build this as a terminal: ideally the station box would be built and then tunnels would be built to all four destinations, making two two-track lines.

The length of this station should be 300 meters, to accommodate 12-car trains, but if it’s too hard to build within the available footprint, then a shortening to 10- or even 8-car trains is feasible. Regional trains in both Paris and Tokyo are usually only 200 meters long. In addition, unlike its Parisian inspiration, Chatelet-Les Halles, Fulton Street need not have very wide platforms. When I took the RER A and changed trains at Chatelet, at 8:40 in the morning, the platform was about as crowded as that of a normal subway station, and needed much less than its full width of 17 meters. Indeed, the Chuo Line, with far higher peak load than anywhere in the West, terminates on a single 10-meter-wide island platform. A single-level four-track station with a cross-platform transfer should be about 30-35 meters wide; since it is too wide for most Lower Manhattan Streets, another option is a bilevel station with two tracks per level, with useful cross-platform transfers, and about 15-18 meters wall to wall per level.

The best time to have built this project was right after 9/11. Because of the connection to World Trade Center, it could have been funded out of 9/11 recovery funds, which instead went to the Calatrava PATH terminal. In addition, the rebuilding of WTC and the PATH terminal could have been done in tandem with the new train station, making its placement far easier. Alas, this did not happen, and all available space east of the WTC site is gone.

The difficult part in building this is the train station, not the access tunnels. Access tunnels can be built very deep using tunnel-boring machines and can even go directly underneath existing subway tunnels. For example, Paris Métro Line 14, whose construction cost was low relative to its depth and Paris’s underground complexity, goes parallel to and under Line 7 for a short segment, and a few kilometers of the RER D were constructed alongside the preexisting RER A tunnel. While I’m not aware of similar examples outside Paris, this shows that it is doable. In contrast, I don’t know of new stations built right underneath preexisting stations in parallel except for some high-cost US projects like the BART Market Street Tunnel Sixth Avenue Subway (thanks to Adirondacker for the correction). Stations-under-stations in oblique configurations exist in Paris, but the biggest station, namely Chatelet-Les Halles, avoids this.

The upshot is that many streets in Lower Manhattan are suitable for new tunnels, and it’s even possible to have access tunnel go deep under building foundations. However, since nearly all suitable north-south streets already host subways, a new station is more difficult. The option for a station under an existing subway station exists, but would be expensive. Let us then scout alternative locations.

Although it’s desirable to have cross-platform transfers, this configuration is more difficult than a cross configuration, in which the Brooklyn-New Jersey line goes east-west in Manhattan. This is because under a north-south configuration it may be difficult to have the Brooklyn-New Jersey tracks dive and turn west fast enough to connect to the desired New Jersey end. An east-west configuration also permits narrower single-level station caverns.

Finally, we should consider the fact that peak employment in Lower Manhattan is around Wall Street, judging by where skyscrapers are located, whereas the main station to connect to is at Fulton Street. In both cases, the key location is well east of the WTC site. Thus a Cortlandt Street location is suboptimal, and a West Street location, where there’s enough space for everything, is too far away. We will repeatedly look at the location relative to existing subway stations in Lower Manhattan: close is good, intersection is not so good.

With the above in mind, here are the options:

East-West Lines

Liberty Street

Advantages: wide enough for everything for a long stretch, from Cortlandt to beyond William. A possible 18*300 box exists from Nassau to Cortlandt, requiring demolition of at most a few low-rise buildings west of Church Street; another box with a slight curve exists from Church to William. There’s a 200-meter stretch that’s 25-meter wide from building edge to building edge. Zucotti Park permits a main entrance with enough space for pedestrians that commuters wouldn’t saturate the neighborhood’s narrow streets. Liberty is close to quite close to the center of Lower Manhattan. Brushes off against the existing Cortlandt Station on the R, but stays away from the other subway stations.

Disadvantages: far from Fulton Street (200 meters); closer to the Wall Street subway station than to the Fulton Street station on the 2/3 and J/Z. Also far from one of the easiest if not the most convenient locations for a north-south line. (But see at the end of the post for update.)

Vesey Street

Advantages: one block from Fulton. There’s an easy location for a north-south line (even a four-track one) next to City Hall, right north of Vesey. St. Paul’s Churchyard can act as the equivalent of Zucotti Park for the Liberty option. Intersects just one subway line, the E. There’s a very easy 200-meter box beginning at Broadway and continuing east.

Disadvantages: far from where most Lower Manhattan workers want to go to. A 300-meter box requires going under Vesey north of WTC, where building foundations may be a problem, or through narrow right-of-way under Ann. Continuing west requires threading the narrows between 1 WTC and 7 WTC, and continuing east requiring threading the Ann Street narrows.

John/Dey Streets

Advantages: one block from Fulton. Almost as close to where most people work as Liberty. Close to the Fulton Street stationhouse, which may be developed into a major retail destination because of the subway station.

Disadvantages: even a 200*15 box would require a few low-rise demolitions. To the east it could thread the John Street narrows, but to the west it would dip under WTC foundations and the memorial. A 300-meter box is impossible without going under skyscraper foundations (fortunately, nothing supertall). Crosses right under the J/Z and 4/5, though the active constraint for depth is probably the WTC foundations to the west.

North-South Lines

City Hall Park

Advantages: enormous space for everything, including a 35*300 box that misses all building foundations, all subway stations, and possibly all subway tunnels. Can bend to the south under Broadway and go under a mid-rise building to the north. A lot of space for pedestrian circulation both in the park and on Broadway.

Disadvantages: closer to the City Hall subway stations than to Fulton – in other words, located about half a subway stop farther away from the CBD than Fulton, which is already at the margin of the main cluster of skyscrapers. If it were picked, then there would probably be a need for a South Ferry train station serving the southern end of Lower Manhattan, which is about a kilometer from the southern end of this location – and South Ferry is so close to the water the station would have to be deep-level.

Broadway

Advantages: close to everything. The street offers about 21 meters of width until well south of Zucotti Park, which is more than enough for a box, and the only stretch narrower than about 24 is at Fulton and John, where the buildings are lower-rise.

Disadvantages: right under and parallel to the 4/5. If this is a four-track option, then this means putting the station at levels -2 and -3. It’s no big deal by the standards of Chatelet-Les Halles or especially Auber, but the RER A was expensive for its time. And even the Chatelet train box was built between two Métro stations (Chatelet and Les Halles, hence the name) rather than under a station.

Church Street or Nassau Street, taking over a subway line

Advantages: could leverage some existing structures, no interference from the subway for rather obvious reasons; under both options the J/Z would terminate at Chambers, where there are existing tracks for it, and under the Church Street option the R would be rerouted along a short new tunnel (cheap by the standards of what we’re talking about here) and thence the Nassau Street tracks. Nassau is literally in the center of the Fulton Street complex.

Disadvantages: beyond the immense subway disruption this would cause, the tracks are old and have insufficient loading gauge. In addition, Nassau, the less disruptive option and the one that is closer to the peak employment center, is a narrow street and even its two subway tracks are on separate levels (see track map). Existing track geometry may impose unreasonable curves, causing squeal.

Greenwich Street

Advantages: serves WTC. Already has a grand terminal because of PATH, reducing the likelihood that politicians will spend billions on starchitecture. I believe that when the street is remapped after WTC construction is complete, it will be 18 meters wide from building to building, permitting an ample train box, even a four-track bilevel one. There’s an easy way to continue both north and south, allowing shallow construction, right underneath the 1 and PATH.

Disadvantages: too far west of where most Lower Manhattan employment is. The PATH terminal may impose unreasonable constraints. Taking over the 1 is a possibility, but presents the same difficulties as taking over the R or J/Z, and would also require an additional South Ferry station, at great depth. The proximity to WTC means the national security agencies may shit bricks about such good transit designs as shallow platforms, maximally free pedestrian circulation, and an open station. Of course the TSA and associated paranoid agencies should be (and is) fought whenever it is required, but ideally agencies should avoid situations that invite a fight they may lose.

Pearl/Water Street

Advantages: Pearl is wide enough for everything north of Fulton, and Water is wide enough south to Pine but with a 22-meter narrows between Fulton and John. Free of obstructions, as the only intersecting subway line, the A/C, is already deep. Can continue south fairly easily as well as north, curving west under the Brooklyn Bridge ramps.

Disadvantages: far east of the existing train station – 300 meters just to the 2/3 at Williams. On a similar note, east of most development; the block east of Pearl and north of Beekman is a parking lot. Conflicts with Second Avenue Subway Phase 4, but this is a small problem as the box could be built with provisions for a two-track subway underneath at little additional cost.

Gold Street

Advantages: close to both the subway station and most Lower Manhattan development. Crosses the A/C line but no station. Can continue north very easily because of the Brooklyn Bridge ramps.

Disadvantages: some room to the north of Fulton, away from the development, but very little south of Fulton; even 250*15 would brush up against the southern end of the street, which is flanked by skyscrapers. In a similar vein, continuing south requires bending west under William or maybe east under Pearl, and both require tunneling under buildings with three-figure height.

Dutch Street, or between Broadway and Nassau

Advantages: both options offer the ability to thread through some gaps in the skyscrapers, going under lower-rise buildings or lower-rise sections of the skyscrapers and limiting the amount of demolition required. Literally at the same site as the subway station. Quite close to most commercial buildings.

Disadvantages: even a 200*15 box would probably require deep-level construction to limit demolitions. Has some leeway to the south and north (assuming shallow construction) but much less than options using continuous streets. In other words, very expensive.

Update: another option is to route the Staten Island-Manhattan tunnel through Brooklyn, in which case it comes into Manhattan from the east, allowing a four-track east-west option. Both Vesey and Liberty present the option of the line to Grand Central branching north under West, then diagonally once deep enough that it can freely go under private property. Vesey presents the additional option of going north under Greenwich, which conflicts with nothing. Conversely, Liberty has the advantage of being south of the 9/11 memorial rather than south of skyscrapers, allowing the turn to West to have much wider curve radius (about 200 meters) without going under any building or the footprint of the Twin Towers.