How Tunneling in New York is Easier Than Elsewhere

I hate the term “apples-to-apples.” I’ve heard those exact three words from so many senior people at or near New York subway construction in response to any cost comparison. Per those people, it’s inconceivable that if New York builds subways for $2 billion/km, other cities could do it for $200 million/km. Or, once they’ve been convinced that those are the right costs, there must be some justifiable reason – New York must be a uniquely difficult tunneling environment, or its size must mean it needs to build bigger stations and tunnels, or it must have more complex utilities than other cities, or it must be harder to tunnel in an old, dense industrial metropolis. Sometimes the excuses are more institutional but always drawn to exculpate the political appointees and senior management – health benefits are a popular excuse and so is a line like “we care about worker rights/disability rights in America.” The excuses vary but there’s always something. All of these excuses can be individually disposed of fairly easily – for example, the line about worker and disability rights is painful when one looks at the construction costs in the Nordic countries. But instead of rehashing this, it’s valuable to look at some ways in which New York is an easier tunneling environment than many comparison cases.

Geology

New York does not have active seismology. The earthquake-proofing required in such cities as Los Angeles, San Francisco, Tokyo, Istanbul, and Naples can be skipped; this means that simpler construction techniques are viable.

Nor is New York in an alluvial floodplain. The hard schist of Manhattan is not the best rock to tunnel in (not because it’s hard – gneiss is hard and great to tunnel in – but because it’s brittle), but cut-and-cover is viable. The ground is not going to sink 30 cm from subway construction as it did in Amsterdam – the hard rock can hold with limited building subsidence.

The underwater crossings are unusually long, but they are not unusually deep. Marmaray and the Transbay Tube both had to go under deep channels; no proposed East River or Hudson crossing has to be nearly so deep, and conventional tunnel boring is unproblematic.

History and archeology

In the United Kingdom, 200 miles is a long way. In the United States, 200 years is a long time. New York is an old historic city by American standards and by industrial standards, but it is not an old historic city by any European or Asian standard, unless the standard in question is that of Dubai. There are no priceless monuments in its underground, unlike those uncovered during tunneling in Mexico City, Istanbul, Rome, or Athens; the last three have tunneled through areas with urban history going back to Classical Antiquity.

In addition to past archeological artifacts, very old cities also run into the issue of priceless ruins. Rome Metro Line C’s ongoing expansion is unusually expensive for Italy – segment T3 is $490 million per km in PPP 2022 dollars – because it passes by the Imperial Forum and the Colosseum, where no expense can be spared in protecting monuments from destruction by building subsidence, limited by law to 3 mm; the stations are deep-mined because cut-and-cover is too destructive and so is the Barcelona method of large-diameter bores. More typical recent tunnels in Rome and Milan, even with the extra costs of archeology and earthquake-proofing, are $150-300 million/km (Rome costing more than Milan).

In New York, in contrast, buildings are valued for commercial purposes, not historic purposes. Moreover, in the neighborhoods where subways are built or should be, there is extensive transit-oriented development opportunity near the stations, where the subsidence risk is the greatest. It’s possible to be more tolerant of risk to buildings in such an environment; in contrast, New York spent effort shoring up a building on Second Avenue that is now being replaced with a bigger building for TOD anyway.

Street network

New York is a city of straight, wide streets. A 25-meter avenue is considered narrow; 30 is more typical. This is sufficient for cut-and-cover without complications – indeed, it was sufficient for four-track cut-and-cover in the 1900s. Bored tunnels can go underneath those same streets without running into building foundations and therefore do not need to be very deep unless they undercross older subway lines.

Moreover, the city’s grid makes it easier to shut down traffic on a street during construction. If Second Avenue is not viable as a through-route during construction, the city can make First Avenue two-way for the duration. Few streets are truly irreplaceable, even outside Manhattan, where the grid has more interruptions. For example, if an eastward extension of the F train under Hillside is desired, Jamaica can substitute for Hillside during construction and this makes the cut-and-cover pain (even if just at stations) more manageable.

The straightforward grid also makes station construction easier. There is no need to find staging grounds for stations such as public parks when there’s a wide street that can be shut down for construction. It’s also simple to build exits onto sidewalks or street medians to provide rapid egress in all directions from the platform.

Older infrastructure

Older infrastructure, in isolation, makes it difficult to build new tunnels, and New York has it in droves. But things are rarely isolated. It matters what older infrastructure is available, and sometimes it’s a boon more than a bane.

One way it can be a boon is if older construction made provisions for future expansion. This is the most common in cities with long histories of unrealized plans, or else the future expansion would have been done already; worldwide, the top two cities in such are New York and Berlin. The track map of the subway is full of little bellmouths and provisions for crossing stations, many at locations that are not at all useful today but many others at locations that are. Want to extend the subway to Kings Plaza under Utica? You’re in luck, there’s already a bellmouth leading from the station on the 3/4 trains. How about going to Sheepshead Bay on Nostrand? You’re in luck again, trackways leading past the current 2/5 terminus at Flatbush Avenue exist as the station was intended to be only a temporary terminal.

Second Avenue Subway Phase 2 also benefits from such older infrastructure – cut-and-cover tunnels between the stations preexist and will be reused, so only the stations need to be built and the harder segment curving under 125th Street crossing under the 4/5/6.

14 comments

  1. Tunnelvision

    Where are you getting your information from, some very sweeping generalizations here- that are somewhat questionable.

    Seismic. New York State Building Code Chapter 16 requires designers to determine the seismic zone in which the structures they are designing sit and then design as appropriate. The last earthquake that hit NY with any real impact was back in 2011, but it is an a seismic zone and this has to be designed for. And yes the Building Code is applied because subway tunnels and stations are considered to be occupied and as such need to comply with the Code, NY State Code because MTA is a State Agency…… not that the NY City code is much different. And quite honestly the design of underground structures does not vary massively whether your in a very seismically active area or not, as this structures will move with the ground in a seismic event. Segmental lining design is virtually the same and the differences are not really major cost drivers. The extras usually come where for example you have to add in a flexible joint to take into account relative ground movements, not used in NY but used on the Avraysa crossing in Istanbul for example or for the Bay Crossing in SF. LA has a separate issue which is the methane bearing ground around the LaBrea Tar pits which requires a radically different and more expensive design to be adopted to exclude the methane from the operating tunnels.

    Manhattan Schist is almost a perfect tunnel excavation material. Not too hard, not too abrasive, brittle helps as it makes it easy to cut with a TBM due to the fracture mechanism, relatively little water and has good stand up time meaning rock support requirements are not excessive. Two downsides, pegmatite dykes which are very hard and the mica content which can trap water. Excellent material for bulk fill for say a park or a golf course, but the mica content means it is hard to compact so limited beneficial reuse but still useable.

    Not sure what you mean by conventional tunnel boring is not problematic for the underwater crossings, and implying Istanbul used different technology. The depth of the water does not in reality impact the technology used as much as the ground conditions do. Assuming the ground is something other than rock the choice of which kind of pressurized face TBM to use, Earth Pressure Balanced, Slurry or Variable Density will depend more on the ground to be encountered rather than the hydrostatic pressure to be encountered. And if the crossing stays in rock then this matters even less. All the hydrostatic pressure does is mean that the TBM’s main bearing seals and Tailskin grouting systems will need to be rated to cope with the pressures. The bigger challenge with water depth is how to get into the cutterhead to undertake cutter tool replacement and maintenance. For example in Istanbul Herrenknecht designed the TBM to have a significant number of its cutting tools able to be changed from within the cutting arms under atmospheric conditions, with limited numbers requiring up to 9 bar saturation diving to access. However the application of this approach is limited by TBM size. Typically standard compressed air working to allow entry to the cutterhead can be performed up to 3 bar pressure, equivalent of 30m depth of water. BUT at that pressure your working time is severely limited as these days your total bottom time is often limited to 4 hours, so say 40 minutes in the air and almost 3,5 hours decompression time to avoid the bends. Even with a double manlock this is inefficient. Mixed gas interventions are also used and saturation diving techniques can be used in the very high pressure situations but these are expensive and risky. TBM manufacturers are looking to automate tool changes but still, handling a 300lb cutter is not easy in the cutterhead. In an ideal world you would have cutting tools that can last for as long as needed with robotic or automated tool changing (if necessary), but we are not there yet and as such interventions to the cutterhead are needed. Where possible these can be planned for good ground areas, or pre treated safe havens but your TBM’s will still need to have the capability for compressed air interventions. Its also prudent to have circumfrential ground treatment holes pre installed in the TBM Shield just in case the ground is so bad you cannot stabilize the face with compressed air, have no surface access but still need to get in the cutterhead, this enables ground freezing to be implemented for example. As such the technology is identical, the main difference would be the segment thickness for hydrostatic pressure and to counter buoyancy, other than that I would expect to see no real difference in the technology between Istanbul and New York.

    As for cut and cover, even where the rock head is high in NY, there is still overlying fill that needs to be excavated through. Plus the rockhead is not high everywhere. Look at the long section of Manhattan and you will notice a section between say 32nd and say Houston where there are not too many high rises, that’s because the rock head dips and your now in glacial tills or similar which requires significant support of excavation to enable excavation to occur. And who wants to have an open cut trash the neighborhood these days anyway.

    Sub surface obstructions and street grid. There is a network of water and sewer tunnels that often dictate elevation of new tunnels in NY, so shallow tunnels are not as easy as you believe. But as designers, its always better to be as shallow as possible as that makes the surface connections cheaper but its not always possible. The street grid is a nightmare, especially getting easements to pass beneath private properties, very expensive and time consuming. Your comments on how easy it is to redirect traffic in NY are somewhat naïve, I take it you have not dealt with NYC DOT to get road closure or even parking lane closure permits…….

    Yes there’s a lot of infrastructure that can be reused, planning for East Side Access had to take into account of and leave provision for future expansion of the subway in the Queens area for example.

    So no New York is not unique, the tunneling techniques and technology used around the world are also used in NY with little difference. Design standards are fairly uniform across the US and the world, concrete is concrete. Utilities, problematic in every big city, NY is no different than anywhere else in that regard and in some respects, the lack of history makes excavation easier compared to Istanbul, Athens, Rome where may shafts were excavated by archaeologists. If you look at the cost to create the underground space, New York is not too bad compared to other US locations. If your going to compare NY to Istanbul for example though don’t, the disruption tolerated in Istanbul would not be tolerated in NY, for example in Gayretepe where the new station servicing the airport metro is being built and a major exit ramp from the E5 highway splits the site offices from a shaft, with staff blithely wandering across the motorway ramp, and I can give you plenty of other examples of the complete don’t give a fuck attitude of contractors in Istanbul. Your also missing the political patronage that exists in many countries, sometime overt sometimes covert. Lose money on a metro project and you get a nice cushy road project in which to make your money back, or a preferential deal on a property development deal. Contractors in Europe operate in a very different environment than in the US and under very different procurement rules.

    I have worked in the tunneling industry for over 30 years, from Channel Tunnel, the Great Belt project in Denmark, through Hong Kong, Istanbul and currently in the US. I undertake peer reviews on designs from our offices across around the world and I have to say that there are not significant differences in the design of the underground space. What goes inside that space is a different issue, but the design for the creation of the new underground real estate varies little from country to country. What does change is the environment your working in, legal and contractual as well as base costs and constraints that your working with. In theory installing a secant pile shaft wall should be the same, but all the base costs in the US will be higher for the equipment, steel, concrete, labor as wages are higher, and the productivity will likely be lower, not because US workers work slower but because the noise ordinance will likely restrict your working hours…. ..prices and costs differ and no matter how hard you try US contractors will never build stuff for the same price as contractors in other countries, its simply not happening…..

    • Matthew Hutton

      If the noise ordinance in New York restricts your construction time more than Western European or East Asian cities then frankly that noise ordinance is absurd.

      Same with contractor health and safety. Yes Turkey might care less about it – but Western Europe and I’m sure Japan, South Korea and Taiwan care about that as well.

      • Matthew Hutton

        And if the New York government or utilities are harder to deal with than those in Western Europe or developed Asia. Well that’s a problem and one that should be fixed.

      • Connor Crowley

        Construction code is a state creation as is the MTA. Blaming construction code is functionally blaming poor specifications by the MTA/state.

    • Alon Levy

      1. In all of our comparison cases (Turkey, Italy, Sweden), the contractors make money on metro construction. Profit rates are much lower than in New York, and Istanbul profit rates are extremely low, but that’s competition, not patronage.

      2. High US wages are not a general fact – working-class wages in the US aren’t especially high (look at retail, for example), it’s just that Swedish contractors hire workers from all over Sweden and all over the EU and New York contractors can only hire New Yorkers.

      3. Yes, American procurement rules are broken – that’s my point.

      4. Stockholm has strict noise ordinances as well, it’s just less relevant when you’re drill-and-blasting than when you’re using a TBM.

      5. The fill is softer than the rock, yes, but as I understand it the TBMs went in schist for phase 1 – and the fill is still much easier to cut-and-cover in than the pain that is Amsterdam. Milanese ground is as I understand it not great for tunneling (Naples is the worst, hence higher costs than in the rest of Italy – it’s not the mafia).

    • Nilo

      “As for cut and cover, even where the rock head is high in NY, there is still overlying fill that needs to be excavated through. Plus the rockhead is not high everywhere. Look at the long section of Manhattan and you will notice a section between say 32nd and say Houston where there are not too many high rises, that’s because the rock head dips and your now in glacial tills or similar which requires significant support of excavation to enable excavation to occur. And who wants to have an open cut trash the neighborhood these days anyway.”

      This is not a true statement. NYC doesn’t haves skyscrapers there due to zoning, nothing else.

      • Tiercelet

        So this is interesting. I am seeing pretty convincing arguments (e.g. https://buildingtheskyline.org/bedrock-and-midtown-i/) that economics, rather than construction feasibility, was the determining factor for skyscraper location–with the obvious caveat that those aren’t strictly separable, since worse building conditions raise the expense and make the economics worse, even if it’s technically feasible to do.

        That said, even if we dismiss the “skyscrapers in NYC cluster because of the bedrock” thing as a myth, it still appears to be true that the bedrock *is* much more deeply buried between, say, City Hall and 14th St. than it is around Wall St or in Midtown. I can only take at the commenter at their word that this makes tunneling more expensive and difficult.

        In any event, I think the operative part of the quote is really the last part: “who wants to have an open cut trash the neighborhood these days anyway.” It points right back to a regular theme, the power of noisy (frequently very wealthy) local residents to use their temporary inconvenience to veto infrastructure development that would benefit the whole rest of society at large.

        • Henry Miller

          There are lots of ways to build shallow subways that are about as cheap as cut and cover without being as disruptive. There will be some surface disruption, but it can be minimized if you look at the various options others have tried. You might even be able to innovate on those.

        • Matthew Hutton

          I don’t think the very wealthy are blocking this stuff. Fundamentally you could leak it to page six and they’d look ridiculous. Doubly so if they happened to be out of town a lot during construction.

          Most likely the issue is the coop board presidents and similar people who live in the city full time – and the MTA and other public sector bodies just need to make an effort to handle those people. My experience is that they don’t even try and deal with them constructively – even in cases where those people would clearly benefit from the project in question.

  2. adirondacker12800

    Want to extend the subway to Kings Plaza under Utica? You’re in luck, there’s already a bellmouth leading from the station on the 3/4 trains.

    Just because it seemed like a good idea in 1910 doesn’t mean it is a good idea today. They didn’t think was a good idea by 1925. There is a stubby little chunk of station OVER the Utica Ave. station on the Fulton line for the Second System tracks.

  3. A. Paddock

    It’s the American condition: excuses, excuses, excuses. Where once Americans would move Heaven and Hell to find a way to get things done, the attitude it now, effectively, “Oh well. It can’t be helped. Why bother trying?” I get so tired of hearing it. We used to build stuff. All around the world stuff is getting built. If everyone else can figure it out and we did once upon a time, then why not now? No vision, no boldness, no willingness to try, total pessimism about possibilities, and a tenacious resistance to changing their minds. No wonder magical thinking is so common now. People don’t even pray as much — not that God has the best record of answering prayers. It’s really depressing. It’s frustrating, too, that things people in so many countries can take for granted is practically impossible here.

    • Nathanael

      Agreed — the American can’t-do attitude is irritating me. Excuses, generally bogus excuses, rather than rolling up the sleeves and figuring out how to fix the problem.

      I live in a can-do city in upstate NY. NYC is very, very “can’t-do” by comparison. It’s astonishing. The way the MTA spent THIRTY YEARS making excuses for blatantly violating the ADA, and then had to be sued into oblivion to be forced to actually follow the law, is an example of the can’t-do attitude.

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