It is relatively easy to come up with a database of urban rail lines and their construction costs per kilometer. Construction costs are public numbers, reported in the mass media to inform citizens and taxpayers of the costs of public projects. However, the next step in understanding what makes American construction costs (and to a lesser extent common law construction costs) so high is breaking down the numbers. The New York Times published an excellent investigative piece by Brian Rosenthal looking at why Second Avenue Subway specifically is so expensive, looking at redundant labor and difficulties with contractors. But the labor examples given, while suggestive, concern several hundred workers, not enough for a multibillion dollar cost difference. More granularity is needed.
After giving examples of high US construction costs outside New York, I was asked on social media whether I have a breakdown of costs by item. This motivated me to look at station construction costs. I have long suspected that Second Avenue Subway splurged on stations, in two ways: first, the stations have full-length mezzanines, increasing the required amount of excavation; and second, the stations were mostly excavated from inside the tunnel, with only a narrow vertical access shaft, whereas most subway lines not crossing under older lines have cut-and-cover stations. The data I’m going to present seems to bear this out.
However, it is critical to note that this data is much sparser than even my original post about construction costs. I only have data for three cities: New York, London, and Paris.
In New York, Second Avenue Subway consisted of three new stations: 96th Street, 86th Street, and 72nd Street. Their costs, per MTA newsletters: 72nd Street cost $740 million, 86th Street cost $531 million, 96th Street cost $347 million for the finishes alone (which were 40% of the costs of 72nd and 86th). MTA Capital Construction also provides final numbers, all somewhat higher: 72nd Street cost $793 million, 86th Street cost $644 million, 96th Street cost $812 million. The 96th Street cost includes the launch box for the tunnel-boring machine, but the other stations are just station construction. The actual tunneling from 96th to 63rd Street, a little less than 3 km, cost $415 million, and systems cost another $332 million. Not counting design, engineering, and management costs, stations were about 75% of the cost of this project.
In Paris, Metro stations are almost a full order of magnitude cheaper. PDF-p. 10 of a report about Grand Paris Express gives three examples, all from the Metro rather than GPX or the RER, and says that costs range from €80 million to €120 million per station. Moreover, the total amount of excavation, 120,000 m^3, is comparable to that involved in the construction of 72nd Street, around 130,000 m^3, and not much less than that of 86th Street, around 160,000 m^3 (both New York figures are from an article published in the Gothamist).
A factsheet about the extension of Metro Line 1 to the east breaks down construction costs as 40% tunneling, 30% stations, 15% systems, and 15% overheads. With three stations and a total cost of €910 million over 5 km, this is within the range given by the report for GPX. The tunneling itself is according to this breakdown €364 million. An extension of Line 12 to the north points toward similar numbers: it has two stations and costs €175 million, with all tunneling having already been built in a previous extension. Piecing everything together, we get the following New York premiums over Paris:
Tunneling: about $150 million per km vs. $90 million, a factor of 1.7
Stations: about $750 million per station vs. $110 million, a factor of 6.5
Systems: about $110 million per km vs. $35 million, a factor of 3.2
Overheads and design: 27% of total cost vs. 15%, which works out to a factor of about 11 per km or a factor of 7 per station
Rosenthal’s article documents immense featherbedding in staffing the TBMs in New York, explaining much more than a factor of 1.7 cost difference. This is not by itself surprising: Parisian construction costs are far from Europe’s lowest, and there is considerable featherbedding in operations (for example, train driver productivity is even lower than in New York). It suggests that Paris, too, could reduce headcounts to make tunnel construction cheaper, to counteract the rising construction costs of Grand Paris Express.
But the situation with the stations is not just featherbedding: the construction technique New York chose is more expensive. The intent was to reduce street disruption by avoiding surface construction. Having lived on East 72nd Street for a year during construction, I can give an eyewitness account of what reducing disruption meant: there was a giant shaft covering about half the width of Second Avenue, reducing sidewalk width to 7 feet, between 72nd and 73rd Streets. This lasted for years after I’d moved away, since this method is so expensive and time-consuming. Under cut-and-cover, this disruption would cover several blocks, over the entire length of the station, but it would be finished quickly: the extension of Line 12 is currently in the station digging phase, estimated to take 18 months.
London provides a useful sanity check. Crossrail stations are not cut-and-cover, since the line goes underneath the entirety of the Underground network in Central London. Canary Wharf is built underwater, with 200,000 m^3 of excavation and 100,000 m^3 of water pumped; it’s technically cut from the top, but is nothing like terrestrial cut-and-cover techniques. The cost is £500 million. It’s a more complex project than the comparably expensive stations of Second Avenue Subway, but helps showcase what it takes to build stations in areas where cut-and-cover is not possible.
Another useful sanity check comes from comparing subway lines that could use cut-and-cover stations and subway lines that could not. Crossrail is one example of the latter. The RER A’s central segment, from Nation to Auber, is another: Gare de Lyon and Chatelet-Les Halles were built cut-and-cover, but in the case of Les Halles this meant demolishing the old Les Halles food market, excavating a massive station, and moving the Metro Line 4 tunnel to be closer to the newly-built station. The total excavated volume for Les Halles was about 560,000 m^3, and photos show the massive disruption, contributing to the line’s cost of about $750 million per km in today’s money, three times what Paris spends on Metro extensions. In London, all costs are higher than in Paris, but without such difficult construction, the extension of the Underground to Battersea is much cheaper than Crossrail, around $550 million per km after cost overruns and mid-project redesigns.
The good news is that future subway extensions in the United States can be built for maybe $500-600 million per km rather than $1.5-2 billion if stations are dug cut-and-cover. This is especially useful for Second Avenue Subway’s phase 2, where the segments between the station boxes already exist thanks to the aborted attempt to build the line in the 1970s, and thus cut-and-cover stations could simply connect to already-dug tunnels. It could also work for phases 3 and 4, which cross over rather than under the east-west lines connecting Manhattan with Queens and Brooklyn. The same technique could be used to build outer extensions under Utica and Nostrand in Brooklyn. Among the top priorities for New York, only a crosstown subway under 125th Street, crossing under the north-south line, would need the more expensive station construction technique; for this line, a large-diameter TBM would be ideal, since there would be plenty of space for vertical circulation away from the crossing subway lines.
There would still be a large construction cost premium. Changing the construction method is not enough to give New York what most non-English-speaking first-world cities have: getting down to $200 million per kilometer would require changes to procurement and labor arrangements, to encourage competition between the contractors and more efficient use of workers. Evidently, overheads are a larger share of Second Avenue Subway cost than of Parisian costs. But saving money on stations could easily halve construction costs, and aspirationally reduce them by a factor of three or four.