Talking to Marco Chitti about the history of Italian construction always fills me with hope. He’s been gathering data about metro construction in Milan and Rome, and told Elif, Eric, and me about the issue of building through constrained areas. Historic city centers are constrained because tunneling can damage buildings – the first two lines in Milan, built in the 1950s and 60s at abnormally low costs, caused some damage to buildings, since they involved cut-and-cover under streets only 12-15 meters wide. The good news is that tunneling with a tunnel boring machine is fine now. Stations remain an enormous challenge – but the conversation did fill me with optimism about future construction in cities that were not global imperial capitals 2,000 years ago.
Tunnel-boring machines have advanced to the point of being archeology-safe. Italian heritage protection laws from the 2000s forbid any risk to historic buildings and historic sites, but TBM technology at this point allows preserving artifacts. It involves injecting a gel ahead of the cutting edge, which is not supposed to be a cost-raiser.
The result is that tunneling is cheap. This is not a matter of low wages – in fact, Marco cites higher wages for Italian skilled workers who staff TBMs, up to €4,500 a month net, which rises to about €9,000 gross with social contributions. These are based on a nationwide scale that only weakly varies with location, which helps explain why Naples costs are not low despite the region’s low incomes.
Station construction costs vary immensely by location. In Rome, on the same project, stations in a suburban part of the city might be €60-70 million. This does not mean construction is trivially easy: Rome’s suburbs still often host historic sites, having been home to patrician villas in Antiquity, and in fact the word suburb dates to that era. However, it’s relatively safe, and I don’t think Line C ran into such sites.
Then in the most constrained parts of the city, things are different. The extension plans for Line C deeper into city center have station costs in the €400-600 million range. This is not what things cost everything within Rome, or even everywhere within the densely-built parts of the city. But the Line C extension passes through the most historic sites. An already-under construction segment will go to the Colosseum, and a planned extension deeper into city center is to go to Piazza Venezia, at the Wedding Cake, and it is that station that is projected to cost €600 million.
The reason for the high cost is that it is not possible to do archeology- and building-safe cut-and-cover. Piazza Venezia doesn’t quite have enough room for a cut-and-cover dig of a full-length station. It is fed by a wide street, the Via Fori Imperali, and I asked Marco why not build cut-and-cover there, but he pointed out that the street goes through the historic Forum. It is in fact elevated over the ruins; any cut-and-cover there would endanger the Forum, and is not acceptable.
Without cut-and-cover, the only alternative is to mine the stations. Rome investigated the option of large-diameter TBMs on the Barcelona L9 model and found it infeasible, since the tunnels are so big they might themselves cause some building damage. Once the stations are mined from a small shaft, their costs explode. Second Avenue Subway built stations using the same method, and had similar per-station construction costs.
The good news
Mined station construction is in practically all cases not necessary. New Yorkers talk about the city’s high built-up density as a reason why costs are high. But in terms of actual stuff in the way of a tunnel, there’s less in New York than in Rome or Istanbul, which has even lower construction costs.
In fact, there is a line in Rome that is rather similar in urban geography to Second Avenue Subway: the Line B1 branch. It runs under a 27 meter wide street flanked by modern buildings that are about 9 stories tall above ground but also have underground parking, Italy having such a car culture that the middle class expects to own cars even in Rome. The cost: €527 million for 3.9 km, in 2010-15.
Moreover, the hard rock in New York should make it easier to build stations while maintaining building safety. Manhattan’s schist is brittle and therefore requires concrete lining, unlike the more uniform gneiss of Stockholm, famously forming natural arches that are pretty to look at from within the tunnels. However, it is still better soil for construction than the sand of Berlin’s U5 extension, to be opened next month, or the alluvial soil of Amsterdam.
The explanation Marco gives concerning station construction is physical and not institutional. This means it should transplant well into another setting – which it does!
In Berlin, the city-center U5 extension, including U55, is in today’s money around €240 million/km. The stations look like cut-and-cover to me, and if they’re not then it comes from severe NIMBYism since the line goes under the very wide Unter den Linden, but one of the stations is basically under the river and another is under U6 and involves moving the U6 station, and the sandy soil is genuinely bad to tunnel through. Suburban extensions in Berlin, with easy cut-and-cover stations, are consistently in the €100-150 million/km range, which is barely higher than the non-Forum Italian range. So Berlin looks fine, and just needs to invest resources into U- and S-Bahn extensions and not into extending the A 100 motorway.
Can New York have what Italy has?
Almost certainly! Second Avenue is not an old or narrow street by Italian standards. Nor are any of the other streets slated for subway construction in New York, such as Nostrand, Utica, and even 125th. Importing construction techniques from Italy and Germany should be feasible. There may be problems with local politics – New Yorkers absolutely hate admitting that another city may be better than theirs in any way, and this makes learning harder. But it is not impossible, and so far there do not seem to be any physical or economic obstacles to doing so.