Over the last few decades the internet has moved from dial-up to high-speed, cables to wireless, and now it's moving into the sky and underground. Today most major cities with subway systems—Tokyo, Hong Kong, Paris, London, and many more—are adding Wi-Fi to underground stations.

It's easy to pass over the technical difficulty of this modern-day miracle but thanks to temperature fluctuations and exposure to water, getting the internet under all those layers of concrete is even harder than you'd think. It's a far cry from setting up an AirPort router in the living room.

To learn more, we turned to New York City. Its subway system is huge and runs 24/7, with no downtime for maintenance much less Wi-Fi installation. As such, the rollout of its underground internet is still very much a work in progress. The hope is that all 279 underground stations will be connected by sometime in 2017.

Transit Wireless is overseeing the Wi-Fi rollout in NYC, and according to its director of engineering Nathan Cornish, there are a few major differences between above- and below-ground service. "We treat [underground environments] like a bit of a coffin," Cornish says. There's no existing coverage or infrastructure to speak of down there, so Transit Wireless has to build everything from scratch. Each station needs antennas, access points, backup power, and a remote unit that distributes cellular service throughout the platforms. To hook all that up to the actual internet, Transit Wireless also installs fiber optic cables connect each individual station to a central hub referred to as the "base station hotel" where the internet is piped in from the outside. New York's subway system is so large that there will eventually be five of these throughout the city.

"We have guys working down there while there are live trains going through the system and people on the platform."

The hardest part of that installation? Finding a good time to do it. Transit Wireless employees don't have the luxury of just shutting down subway stations for installation, Cornish explains. "We have guys working down there while there are live trains going through the system and people on the platform."

And while getting the internet underground is hard enough, making Wi-Fi work on a subway platform in particular is even harder. Despite being enclosed and technically indoors, the subway is actually considered an "outdoor environment." According to Cornish, subway temperatures can fluctuate from below freezing to over 100 degrees. That's a huge difference from putting an electronic system into an office building, which may never change more than ten degrees year-round, depending on who's got control of the thermostat.

Subway temperatures can fluctuate from below freezing to over 100 degrees

The other problem is water. And not just puddles or errant drips from street-level. "The entire stations are pressure hosed," Cornish says, not that you would necessarily think that when you go down there. But electrical components don't get special treatment in the subway station; they need to be able to handle the hose. Add to that a persistent sprinkling of brake dust—particles of metal sprayed into the air all day as trains pull into the station—and you can see why you'd need some seriously rugged equipment.

NYC's Wi-Fi project is coming along, but other cities already have it beat. In 2007, Hong Kong and Buenos Aires became the first cities to install Wi-Fi in their subway systems. Today, Hong Kong's subway is fully connected, while Buenos Aires has only 13 of 84 stations connected, despite early plans to the contrary. Complications are unfortunate but inevitable. There are plenty of places for rollout to get hung up. Every subway station in unique in terms of depth and layout. Unfortunately that requires creating an individual design for each, and in New York, Cornish notes, that means each and every station has to be approved separately. "There's a significant amount of engineering and project management behind each station's design and approval." It's a long and arduous process that has to be completed long before the actual wiring begins.

While being disconnected underground may cut into your Facebook time, subterranean internet has its upsides as well. A 2014 Gallup poll showed that the average American with a full time job worked between 44-49 hours a week. The workday bleeds into the rest of our lives thanks in large part to round-the-clock email, texts, and other forms of communication. It's a well-covered issue. From Monday through Friday, your average 50-minute daily commute might be your only true respite. Sure, internet will certainly make it easier to stomach getting stuck at the station, but it'll hurt when you get that email from work just as you're descending the steps. So try to enjoy the freedom of zero bars while you still have the chance. It won't last long.

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