Government Technology

Under the Sea


March 2, 2006 By

The San Francisco Bay Area has garnered a reputation as a premier locale for high-tech innovation. Residents can count on being connected virtually anywhere they go -- thanks to the gee-whiz gadgetry of nearby Silicon Valley.

The Bay Area consists of three major cities -- San Francisco, San Jose and Oakland -- and their many orbital suburbs. The community is connected in another vital way as well. From the coastal cities of Richmond, Oakland and San Francisco to inland cities such as Fremont, Concord and Pleasanton, the Bay Area's public transportation system is considered by many to be a lifeline for residents and visitors alike.

Bay Area Rapid Transit (BART) has been a mainstay since the first passengers boarded in 1972. Since then, BART has grown with its passengers and expanded to meet their needs. Still, the blistering pace of technological advancements requires BART to adapt faster than ever before.

Making Connections

Much of the Bay Area boasts wireless connectivity. Powerful cellular signals beam voice and data access to thousands, and almost every coffee shop, office building and shopping center sports a Wi-Fi hotspot. Even BART passengers can use their mobile devices to wirelessly access e-mail, the Internet or other applications ... unless they're in a tunnel.

There are more than 30 miles of subterranean track in BART's rail system. The longest tunnel is also the most vital: The Transbay Tube, which stretches 135 feet below the icy waters of the bay, connects Oakland and San Francisco via 3.6 miles of track, tunnel and darkness. For commuters, wireless access on BART ends as soon as the train plunges below the ocean depths -- cellular signals simply cannot penetrate the sea and soil to reach passengers.

Chuck Rae has been with BART since opening day and currently serves as telecommunications revenue manager. As the technology became available, Rae said BART began considering how to provide wireless access underground.

"Above ground, your wireless providers pretty much cover transit systems just by virtue of the cell sites being in close proximity," Rae said. "[The difficulty begins] when they hit the underground tunnels."

The solution was a distributed antenna technology known as Radiax. BART has used Radiax cables for years to maintain internal communications on train radio. Adapting the Radiax technology to handle subterranean cellular communications puts BART at the forefront of underground wireless connectivity.

Rae explained how the first four BART stations were connected -- and eventually how the entire Transbay Tube will be.

"Think of Radiax as coaxial cable with leaky holes in it," Rae said. "It's a fat co-ax with a lot of windows in it. We call that a distributed antenna. Instead of antenna every 6 inches, you use this cable and that's the distributed antenna. The RF [radio frequency] leaks out and comes [into the train]. It's a simple system really."

To prove to a skeptical board of directors that the need existed, Rae and his staff surveyed BART passengers in early 2001.

"We did an actual passenger survey and it came back favorably that the majority of people would like to see it," he said. "[BART] did a phone survey and actually did one by interviewing people in the stations. So it was a good sampling of the patrons.

"Then when 9/11 hit, I think it magnified it in the sense that it would be nice to have communications in case something did happen."

In 2002, BART sent out an RFP requesting that a telecommunications company finance and develop an underground wireless system for BART tunnels. At the time, BART employed a third-party developer, the Andrew Corp., makers of Radiax, as part of the RFP, which resulted in telecommunications companies balking at the opportunity. No one committed to the project.


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