There are about 200 rooms crammed full of relays scattered around the system, and most observers agree they work remarkably well. Because they don’t do anything more complicated than open and close, relays can last decades before needing replacement; some of today’s models went into service before the Great Depression. “You could run the system like that for another 400 years, no problem,” one subway worker assured me.

The weakness of the relays is the wiring that leads up to them, which dates to the thirties and is wrapped in cloth so decrepit that it burns when ignited. Worse, those wires carry a searing 120-volt power supply, ten times more powerful than modern wires. When firefighters showed up to quench the Chambers Street blaze, they couldn’t use their hoses because the wiring was still live, and there was no central switch to turn it off. Transit workers had to painstakingly trace each wire back to its source and cut it manually. “Everything is hooked up to everything else. It’s an old design,” says Tracy Bowdwin, the assistant chief signals officer. The NYCT has slowly been replacing the stuff, but 41 of 200 relay rooms still use antique wiring. It won’t all be gone until 2023.

Until then, are we at serious risk of another huge, subway-halting fire? Depends on whom you believe. Reuter argues that the chances are very slim; the A-and-C fire was only the second of that nature in the subway’s entire history, with the other being a rollicking blaze that destroyed a relay room at the Bergen Street station in 1999, when water caused a short. But George McAnanama, a Transport Workers Union official, disagrees. “It’s obvious that the problems they had in the Bergen Street fire are not corrected. These fires are not an isolated event.” He says workers encounter about 100 smaller fires a month, most of which the public never hears about because the Fire Department is rarely called: “If you call the FDNY, you have to stop service. So they get subway workers to take care of the little ones.”

Another problem associated with the relays is what happens if we run out of them. Fifty-seven replacement parts had to be installed after the A-and-C fire, and according to Bowdwin, the MTA has only a few hundred backups, depending on the model, and only a tiny handful of companies worldwide still make them. If we had another big fire, observers say, we could find ourselves back-ordered on the parts—and stuck in the meantime with a subway line moving like molasses.

The subway is always inherently falling apart—rigorous maintenance is the only defense against the natural pull of entropy.

These dilemmas are partly why the NYCT plans to replace the relay system with Communications-Based Train Control. Pioneered in the Paris subway, this system tracks the location and speed of trains with radio tags and onboard lasers. Engineers get a precise computer map of where every train is, which enables them to run trains far closer together than they can under the current relay-based system. Reuter figures it’ll boost subway capacity by as much as 25 percent, which is more than the entire projected Second Avenue subway.

There are also new techniques to mitigate the problem of riders’ delaying the trains by holding doors open. Currently, on most trains, if someone jams his hand in the door, the doors open wide to let him in. New doors are controlled by software that can open them just a few inches—enough for him to get his hand out, but not enough to get inside the train. Since hand-jamming will no longer be a way to stop a train, the MTA hopes to eventually wean people off the habit entirely. “You save five seconds with every train. That doesn’t seem like much, but that’s two minutes an hour—enough time to run another whole train,” says Bob Olmsted, a former director of planning for the MTA.

Neat stuff. By the time it’s fully in place, though, you’ll be in an old-age home: The MTA’s upbeat estimates say it’ll take 30 years to finish the work. If there were plenty of cash, it might be possible to do the work faster. But on a system that needs to run 24/7, rehab work is inherently slow; workers literally have to scurry between moving trains. The NYCT picked the L line as its first experiment with the new communications system, and it has taken five years of preparation to bring it online this summer. Currently, it’s in the debugging stage, according to project manager Nabil Ghaly, and there have been some strange bugs. One engineer in Queens discovered that boys playing with remote-controlled toy cars interfered with the trains’ signals.

Assuming all goes well, the relays on the L line will be retired by the end of year, at which point the NYCT also plans to get rid of conductors on the trains, leaving only one motorman on each. This latter fact has put noses out of joint in the transit union, for obvious reasons of job loss. But McAnanama, the union rep, also warns that cutting staff onboard trains could affect public safety.