The Bay Bridge will close tonight for five days, a disruption that could cause lengthy traffic delays for North Bay drivers heading toward San Francisco over the Labor Day weekend.

Those who can avoid the City and stay north of the Marin County line, however, should be rewarded with relatively open roads.

"Drivers in Sonoma County can be grateful that they are up there," said Randy Rentschler, public affairs director for the Metropolitan Transportation Commission, the Bay Area's transit authority.

The Bay Bridge will close at 8 p.m. tonight, allowing crews to add the finishing touches on the new $6.4 billion eastern span. Work involves paving, striping and removing barriers, bridge officials said. The new side-by-side section will open Tuesday morning at 5 a.m.

Heavy traffic is expected through Marin County as many drivers will use the Richmond-San Rafael Bridge and the Golden Gate Bridge to travel between the East Bay and San Francisco.

"People should be patient," said Kary Witt, manager of the Golden Gate Bridge. "Get an early start."

The Golden Gate Bridge will open the usual four lanes in commute directions on Thursday and Friday and three lanes in each direction over the weekend, Witt said.

Golden Gate Ferry service between Larkspur and San Francisco will add an extra late night trip on Friday and four extra trips on Saturday and Sunday. Some Bay Area Rapid Transit trains will operate on 24-hour schedules from Thursday through Monday.

Sonoma County Airport Express will operate a normal schedule of buses to San Francisco and Oakland airports but could add buses if needed, general operations manager Tony Geraldi said.

"I'm an optimist," he said. "During past Bay Bridge closures, we have had virtually no effect."

In the North Bay, traffic bottlenecks are expected on Highway 101, especially on Thursday and Friday. Choke points include Sausalito north of the Golden Gate Bridge and in San Rafael at Sir Francis Drake Boulevard, transit officials said. Traffic should be normal in Sonoma County.

"I really do not expect to see an impact in Sonoma County," said James Cameron, deputy director of the Sonoma County Transportation Authority. "You should be fine unless you are leaving the area."

Highway 37 is a good alternative route to reach the East Bay, Cameron said. Sonoma Raceway at Sears Point has a light weekend schedule.

Bay Area transportation officials are preparing for the longest Bay Bridge closure since the 1989 Loma Prieta earthquake collapsed part of the bridge, closing it for a month and prompting the replacement of the now 77-year-old double decker truss section.

Officials planned the closure around Labor Day weekend when traffic is usually light. The 49ers and Raiders both play out of town on Thursday. The Giants have a weekend series in Arizona while the A's host Tampa Bay from Friday to Monday.

This is the fifth closure since construction began in 2002. The last shutdown in 2009 lasted three days.

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