SAN FRANCISCO (CBS SF) — The BART Board of Directors awarded a $267 million contract Thursday for seismic retrofits to the Transbay Tube, work that could cause service disruption to riders between Oakland and San Francisco for more than two years.

While BART officials stressed that the 3.8-mile tunnel can currently withstand a large earthquake, the proposed upgrades would make it able to withstand the kind of catastrophic earthquake only expected to hit the Bay Area every 500 or 1,000 years.

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The work would involve installing better interior liners as well as the installation of a new pumping system.

The $267,083,110 contract was awarded to the lowest of three bidders, a joint venture of Oakland-based Shimmick Construction and Pleasanton-based California Engineering Contractors. Funding for the project will primarily come from earthquake safety improvement bonds authorized by voters in 2004.

Work on the upgrades would begin in July 2018 and could take up to 2-and-a-half years. But BART management said it could go faster if there are temporary cuts to service at night and early in the morning.

The work would take place during the overnight hours before service opens Monday through Friday, but to extend the available working hours, the agency is considering having only a single track open in the tube after 9:30 p.m. and to open service an hour later, at about 5 a.m.

The reduced service could help the work be completed four months faster and save nearly $15 million but would affect thousands of daily riders.

More than 2,600 people who take BART between 4 and 5 a.m. would need to make other arrangements.

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Those riders are disproportionately low-income and minority:

during the first hour of service, 66 percent of riders are minorities, compared to 56 percent over the entire day, and 37 percent make less than $50,000 a year, compared to 26 percent during the rest of the day, according to BART.

Most of those riders board at the furthest stations, such as Pittsburg/Bay Point or Dublin/Pleasanton, and head to stations in downtown San Francisco.

Director Joel Keller, who represents the area around the Pittsburg/Bay Point station, said that he was concerned with the impact the decision would have on his constituents and wanted an extensive outreach program before any such mitigation efforts were implemented.

“These are not the stock brokers coming from central Contra Costa County,” Keller said. “These are working people going into the Bay Area to provide service.”

While the contract was approved today, the BART board did not make a decision on the service impacts. But the directors agreed that the safety of the system was paramount, even for such a rare event.

“The Transbay Tube is the heart of our system, if it’s not safe and reliable, we don’t have a system” said Director Gail Murray, who represents central Contra Costa County.

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