More than 100 feet below the roiling waters of the Bay lies BART’s Transbay Tube, one of the region’s most impressive engineering feats — a path that acts as a portal for nearly 200,000 passengers travelling each day between the East Bay and San Francisco.
Tucked neatly into a protective trench on the floor of the Bay, the tube is nonetheless exposed to the elements of corrosive saltwater, and, more troubling, an occasional misplaced ship anchor.
To arm the tunnel’s exterior against the harmful effects of saltwater, the BART tube includes a series of “anode” that are connected by cables along the top of the structure. The electrical charge of the anodes helps convert the steel shell of the tube into a protective layer that doesn’t react negatively to the saltwater, preventing corrosion from eating into the structure.
However, the 30 anodes on the tube jut out nakedly into the water, and the devices are occasionally bashed by a waylaid anchor from one of the innumerable shipping tankers that arrive and depart daily in the Bay, according to BART Assistant General Manager Paul Oversier. The large ships are not supposed to drop anchor above the site, but incidents still occur occasionally.
Under the current procedures, BART checks the tube monthly as part of its routine maintenance inspection. With that schedule, a busted anode could take weeks for the agency to discover, potentially leaving the steel prone to weakening from corrosion.
Wary of any excessive damage to the 3.6-mile-long structure, BART is embarking on a $900,000 program to have on-call repair services available each time an anode is found to be in need of repair. A team of scuba divers and barge operators will be ready each time BART discovers a broken anode, a contrast from the scramble the agency now has to make for available workers.
The agency is also in the midst of installing a smart grid on the Transbay Tube, a technological advance that will notify inspectors the instant an anode is damaged. The on-call services and the electronic notification services will significantly reduce BART’s response time to any broken anodes, Oversier said at the agency’s board of directors meeting Thursday.
“This is one of those things that is behind the scenes,” Oversier said. “But it’s absolutely vital to maintaining what is arguably our most critical asset, the Transbay Tube.”