Uday Schultz has a thorough post about New York’s subway service deterioration over the last decade, explaining it in terms of ever more generous maintenance slowdowns. He brings up track closures for renewal as a typical European practice, citing examples like Munich’s two annual weekends of S-Bahn outage and Paris’s summertime line closures. But there’s a key aspect he neglects: over here, the combination of regional rail and subway tunnels means that different trunk lines can substitute for one another. This makes long-term closures massively less painful and expensive.
S-Bahn and subway redundancy
S-Bahn or RER systems are not built to be redundant with the metro. Quite to the contrary, the aim is to provide service the metro doesn’t, whether it’s to different areas (typically farther out in the suburbs) or, in the case of the RER A in Paris, express overlay next to the local subway. The RER and Métro work as a combined urban rail network in Paris, as do the S- and U-Bahns in German cities that have both, or the Metro and Cercanías in Madrid and Barcelona.
And yet, in large urban rail systems, there’s always redundancy, more than planners think or intend. The cleanest example of this is that in Paris, the RER A is an express version of Métro Line 1: all RER A stops in the city have transfers to M1 with the exception of Auber, which isn’t too far away and has ample if annoying north-south transfers to the Champs-Elysées stations on M1. As a result, summertime closures on the RER A when I lived in the city were tolerable, because I could just take M1 and tolerate moderate slowdowns.
This is the case even in systems designed around never shutting down, like Tokyo. Japan, as Uday notes, doesn’t do unexpected closures – the Yamanote Line went decades with only the usual nighttime maintenance windows. But the Yamanote Line is highly redundant: it’s a four-track line, and it is paralleled at short distance by the Fukutoshin Line. A large city will invariably generate very thick travel markets, and those will have multiple lines, like the east-west axis of M1 and the RER A, the two north-south axes of M12 and M13 and of M4 and the RER B, the east-west spine from Berlin Hauptbahnhof east, the Ikebukuro-Shibuya corridor, or the mass of lines passing through Central Tokyo going northeast-southwest.
The issue of replacement service
In the United States, standard practice is that every time a subway line is shut for maintenance, there are replacement buses. The buses are expensive to run: they are slow and low-capacity, and often work off the overtime economy of unionized labor; their operating costs count as part of the capital costs of construction projects. Uday moreover points out that doing long-term closures in New York on the model of so many large European cities would stress the capacity of buses in terms of fleet and drivers, raising costs further.
This is where parallel rail lines come in. In some cases, these can be other subway lines: from north of Grand Central to Harlem-125th, the local 6 and express 4/5 tracks are on different levels, so the express tracks can be shut down overnight for free, and then during maintenance surges the local tracks can be shut and passengers told to ride express trains or Second Avenue Subway. On the West Side, the 1/2/3 and the A/B/C/D are close enough to substitute for each other.
But in Queens and parts of the Bronx, leveraging commuter rail is valuable. The E/F and the LIRR are close enough to substitute for each other; the Port Washington Branch can, to some extent, substitute for the 7; the Metro-North trunk plus east-west buses would beat any interrupted north-south subway and would even beat the subway in normal service to Grand Central.
Running better commuter rail
The use of commuter rail as a subway substitute, so common in this part of the world, requires New York to run service along the same paradigm that this part of the world does. Over here, the purpose of commuter rail is to run urban rail service without needing to build greenfield tunnels in the suburbs. The fares are the same, and the frequency within the city is high all day every day. It runs like the subway, grading into lower-density service the farther one goes; it exists to extend the city and its infrastructure outward into the suburbs.
This way, a coordinated urban rail system works the best. Where lines do not overlap, passengers can take whichever is closest. Where they do, as is so common in city center, disruption on one trunk is less painful because passengers can take the other. The system does not need an external infusion of special service via transportation-of-last-resort shuttle buses, and costs are easier to keep under control.