Driving subways into the digital age

Americans today are almost always on the grid. Even in 2015, however, there's one place where people still have to hang up their smartphones: underground subways.

But there's good news ahead for public transportation riders who experience heart palpitations when their connection gets cut off. Several of the country's largest cities are working with the four major cell carriers, Verizon, AT&T, Sprint and T-Mobile, to patch up these digital black holes.

By the end of the year, Chicago's CTA will be the largest subway system in the nation to have full 4G in tunnels and stations. There are also plans to upgrade systems in other cities across the country, from New York to LA.

The changes are underway as improving connectivity underground is becoming more crucial to commuters, who use transit time as an extension of their work day, said Scott Mair, a senior vice president at AT&T.

"Our customers expect to use their devices anywhere they are. And if you see what people do during their commute, they're on their devices," he said. "It's like a second office for them. So we need to be in those places."

An economic boost?

The potential increase in worker productivity makes connecting public transportation more attractive, said Rich Barone, director of transportation programs at the Regional Plan Association. His firm is America's oldest independent urban research organization, which focuses on infrastructure in the New York/New Jersey/Connecticut region.

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"Workers who are on transit for longer than 30 to 40 minutes [already] gain flexibility to be more productive and work," he said.

But connected commuters would also be able to make calls and write emails on the subway—making them even more productive.

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"There's a potential argument for economic benefit," Barone said.

As more of America's workers head underground to get to work, cell and Wi-Fi connectivity will become increasingly crucial. 2014 was a record year for public transportation use, when 10.8 billion trips were taken, according to the American Public Transportation Association. That's the highest since 1956 when 10.98 billion trips were taken—a time when personal cars were far from common.

Why did this take so long?

Systems in international cities such as Tokyo, Shanghai, Seoul and Paris have offered free Wi-Fi and cell service in many underground stations, if not all of them, for several years.

Barone said there are a couple of reasons why it has taken so long for American cities to follow suit.

"We're slow adopters in technology. [We] want to wait and see how it's adopted in other places instead of being on the cutting edge," he said. "New York unfortunately, when it comes to technology, is late to the game. Lots of things that we see happening today have been available for over a decade."

Woman using smartphone in subway
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Not surprisingly, money is another major reason for the lag. For years, transportation agencies struggled to figure out how to afford the infrastructure on limited taxpayer money. Only recently did the private sector begin to show interest in footing the bill, Barone said.

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In Chicago, for example, the four major carriers will bankroll the entire $32.5 million 4G project. Washington, D.C., and New York are also getting interest from the private sector.

Another setback in hooking up subway tunnels with cell and Wi-Fi is the 24 hour, seven day a week systems, such as the one in New York.

"We don't have a lot of windows for folks to go in and do work in the tunnels without disrupting service," Barone said. It's easier to install connectivity in the stations but there's an "added cost to implementing service in tunnels."

"Even if you're a system that shuts down overnight, you still only have four to five hours a night to build that infrastructure," he added.

Progress report

CNBC checked out five of the largest cities to see how far along they are in upgrading the network underground:

New York: So far, only 76 out of 277 underground stations offer cell and Wi-Fi connection. Full 4G coverage in all stations is set to be completed by 2017. The 100th station was plugged into Wi-Fi at the end of March. Wi-Fi in all stations will be available by 2018. Third-party, private contractor Transit Wireless is covering the $250 million bill.

Chicago: In a few months, Chicago is slated to be the nation's largest city to have a subway system with full 4G wireless coverage across its 22 miles of stations and tunnels. It's expected to be complete by the end of 2015. The current 2G subway cell system, installed in 2005, provides limited service … if at all.

Washington D.C.: The top 20 busiest stations were wired for cell coverage in 2009, but full wireless cell service is delayed until December 2015 to prioritize safety upgrades related to the 2009 Red Line crash. The D.C. Metropolitan Area Transit Authority is in talks with the four big wireless carriers to advance cell connection in the tunnels on their bill. As for Wi-Fi, none of the stations or tunnels have hotspots.

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Los Angeles: There's no Wi-Fi or cell service in any of the stations. But Wi-Fi is slated to come to four Red Line subway stations in downtown LA by May. The rollout for cell service for those stations will be completed by August. Connecting all 80 stations will cost an estimated $800,000 and will be finished by March 2017. It has not been finalized who will cover the costs but negotiations are ongoing. There is no plan yet for connecting the tunnels.

San Francisco: BART terminated its Wi-Fi license agreement in December, but riders can still get cell signal in some stations—though it's not guaranteed. BART is evaluating options for new Wi-Fi services but a plan has not been approved. There's a new agreement with Verizon to expand 4G LTE for all major carriers within the BART underground this year. This high-speed data project will include stations and tunnels and will be footed by the carriers.