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The Anatomy of a New York Subway Tunnel

The three inch ledge lining the express track tunnel between 7th and Church Avenue on the F line in Brooklyn is an excellent place to listen to Pink Floyd. Trains occasionally clatter by on the local track just behind a cement wall, the passage is lit, and although the third rail is live it’s easily avoided by walking along the raised path along the wall. It’s just me, the steady drip of rainwater leaking through the grates, the scurrying of rats on the rails, and Great Gig in the Sky on my portable boom box.

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But even walking the rails doesn’t give much insight into the impossibly complex workings of the trains. The New York City subway operates 24 hours a day, ferrying over a billion people around this fine metropolis annually. The cars roll seemingly effortlessly in and out of the stations, but in reality there is a world of maintenance required just to keep them dry.

Being below the water table, the subway requires more than 700 pumps to remove an average of 13 million gallons of water a day out of the underground. It is estimated that if maintenance ceased for a mere 36 hours, the tunnels would fill with water. 150 more years of neglect and the subway would be transformed into a labyrinth of fast flowing streams, the station ceilings collapsing with the ubiquitous platform columns which also support the streets above. As New York’s underground disintegrated, it would take the aboveground down with it.

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As it is, not just constant maintenance but a massive amount of electricity is required to keep the trains up and running. Both alternating and direct current are used in tandem to operate signals, lighting, auxiliary equipment, ventilation, and the trains themselves. 2,500 miles of cable pass under 7,651 manholes throughout the city, distributing nearly 500,000 kilowatts through the system during peak hours. In a given year, the subway uses 1.8 billion kilowatt hours — that’s 18 bolts of lightning.

This power is supplied to the trains via the electrified third rail; a wheel, brush, or sliding shoe carries the power from the rail to the train’s electric motor. The third rail carries 625 volts of electricity, enough to fry anyone who so much as pisses on it, let alone touches it.

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The rolling stock (the subway cars themselves) vary in size based on whether they were originally built by the privately owned Interborough Rapid Transit Company (IRT) or the Brooklyn-Manhattan Transit Corporation (BMT).

The IRT’s numbered trains are shorter and narrower than the BMT’s lettered cars. This is explained by the fact that the IRT sections of the track have narrower tunnel segments, tighter curves, and tighter platform clearances than BMT stock, which would have a large gap between door and platform if allowed on the IRT tracks.

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An extensive signal system uses colored lights, infrared sensors, and short-circuits created by the cars’ wheels to prevent crashes. In the original system, train conductors needed a key to reset stop signals in order to proceed (hence the phrase keying by). It is thus that the longest lines with the oldest signal systems are the most often delayed.

So despite every strap-hanger claiming that their local line is the worst, it is in fact F train riders who take the cake — signal delays and malfunctions made the orange line the most delayed of 2013.

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Finally, there are the rails themselves. Made from 39-foot lengths of carbon steel, each rail is 5.5 inches high and 2.5 inches wide. Rolling stock weighing up to 400 tons run them all day, every day, in temperatures ranging from 24 to 102 degrees Fahrenheit, with some sections exposed to the elements year round.

In order to monitor their condition, “geometry trains” travel along the tracks using mounted lasers on their front undersides to take measurements and allow employees to order repairs of any section of track more than 1.25 inches out of alignment.

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The New York City subway is undeniably a feat of engineering, requiring double the annual income of riders’ fares to run. It is the crux of this city, a frequent subject of unbridled obsession, and a subject on which the detail to be studied often feels crushingly infinite.

Yet many, if not most, of us are blissfully happy to ride it without any idea of its functioning. The anatomy of the subway is an electric secret, fully understood only by those who dare walk its tracks and feel its current.

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Read more about the hidden wonders of the world’s subways on Atlas Obscura.