BAY AREA (BCN) -- Bay Area transit agencies are adding service to help  accommodate travelers between the East Bay and San Francisco during this  weekend's closure of the Bay Bridge for seismic retrofit work.

The bridge will close beginning Thursday at 8 p.m. and will remain  closed until 5 a.m. Tuesday, during which time crews will replace a  300-foot-long section of the eastern span of the bridge.

According to Metropolitan Transportation Commission spokesman John  Goodwin, the Bay Bridge typically carries between 250,000 and 280,000  vehicles on weekdays, and 200,000 on the weekends, though Labor Day weekend  numbers are often lower.

Whether the bridge could reopen earlier than Tuesday at 5 a.m. is  still flexible, according to Goodwin.

"If things go well, we would be able to open the bridge early," he  said. "We're not going to know until we're deep into the weekend."

During the closure, BART will operate 24-hours service.

BART service, which normally ends at about midnight, will be  extended throughout the night, running hourly between midnight and 4 a.m. The  changes will be in effect from midnight Thursday until midnight Monday.

However, only 14 of BART's 43 stations will remain open between  midnight and 4 a.m.

In San Francisco, the 24th Street/Mission, Embarcadero and Powell  stations will remain open.

In the East Bay, the Bay Fair, downtown Berkeley, Coliseum/Oakland  Airport, Concord, Dublin/Pleasanton, El Cerrito del Norte, MacArthur, Oakland  City Center/12th Street and Walnut Creek stations will remain open.

On the Peninsula, only the Daly City and San Francisco  International Airport stations will remain open.

During the day, BART will run on a normal schedule, but with  longer trains. Extra trains will also be available to accommodate passengers  headed to sporting events, concerts and shows.

Golden Gate Bridge officials have said that those hoping to detour  through Marin County during the closure period should note the bridge already  operates at capacity on weekends, and there may be significant delays.

Additional Golden Gate Ferry trips between Sausalito and San  Francisco, and from Larkspur to San Francisco will be offered during the  weekend.

Ferry service will also be added between Alameda, Oakland and San  Francisco, as well as from Vallejo, according to Goodwin.

There are currently no restrictions on boat traffic under the  bridge, though the Coast Guard will be monitoring the situation, Goodwin  said.

The bridge closure is part of an overall replacement of the  eastern span of the bridge, scheduled to be completed in 2013, according to  Goodwin. Seismic retrofit work was completed on the western span of the  bridge in 2004.

This weekend, crews operating 150 feet in the air will install a  new 300-foot bridge section, weighing about 3,600 tons, east of Yerba Buena  Island.

Officials plan to remove the existing bridge section at about 1  p.m. Friday, and move in the new section by about 2 a.m. Saturday "if no  unusual difficulties are encountered," Goodwin said.

After this weekend, the next big closure of the bridge will happen  just before the new bridge opens to traffic, according to Goodwin.

"So we don't expect to have to close the bridge again for another  four years," he said.

Caltrans will also use the weekend closure to make improvements to  the toll plaza approaching the bridge from the East Bay.

Crews will demolish a mini plaza used for FasTrak-equipped  vehicles coming to the bridge from Interstate Highway 880 and West Grand  Avenue.

FasTrak customers will still be able to use the lanes approaching  the former mini plaza area, and tolls will be collected with new FasTrak  equipment.
           
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