The Sunset Boulevard bridge is ready for its close-up.

After weeks of preparation, construction crews Friday night will shut down portions of busy Sunset Boulevard and the 405 Freeway on the Westside to begin jackhammering and demolishing the southern half of the bridge. Workers will then spend 10 months rebuilding it before going through the same drill on the bridge’s northern half.

Transportation officials have met regularly with neighbors and businesses, sent e-mail blasts and communicated via Twitter and Facebook to keep them apprised of closures and detours. Still, the project — designed to ease congestion, save carpoolers time and improve safety — promises to wreak a fair measure of havoc for drivers caught unaware as well as for residents who have known for years that this night was coming.

“The longest detour is two miles max,” said Dave Sotero, a spokesman for the Los Angeles County Metropolitan Transportation Authority. “It’s not going to be that large, and it’s going to happen in the middle of the night.”

Sotero said crews will work day and night to rebuild the bridge with 16 pre-stressed concrete girders. When completed, the bridge will be 30 feet wider, a bit higher and better able to withstand earthquakes.

Nonetheless, the prospect fills some Westsiders with dread.

Some people “will be upset no matter what because what you’re dealing with is change,” said Cori Solomon, president of the Brentwood Glen Assn., one of the neighborhoods most heavily affected.

For months, “short-term pain for long-term gain” has been the oft-expressed mantra of the MTA, which is partnering with the California Department of Transportation on the $1-billion-plus project, funded by local, state and federal money.

The project will add a 10-mile northbound carpool lane to the stretch of the 405 between the 10 and 101 freeways through the Sepulveda Pass. The extra lane will allow carpoolers and some drivers of hybrid vehicles to traverse the entire 405 from Orange County to the San Fernando Valley. The project also calls for realigning 27 onramps and offramps, widening 13 existing underpasses and structures and building about 18 miles of retaining and sound walls.

Sunset Boulevard is one of the most heavily traveled east-west roads on the Westside. On average, about 3,500 vehicles cross the 54-year-old Sunset bridge each hour. More than 300,000 drivers travel on the 405 through the Sepulveda Pass each day, officials said.

Demolition-related activities are expected to begin about 9 p.m. on each of six consecutive nights. Ramp closures might begin as early as 7 p.m., the MTA said, with traffic control officers directing motorists onto local streets.

On Friday night, lanes on the northbound 405 will close one by one until all have been shut down. The bridge, freeway and local streets will be reopened starting about 6 a.m. for the daytime travel hours.

Even before the launch of demolition, residents and businesses have been coping with disruptions caused by the project. Concrete K-rails, new striping and sound curtains have dramatically altered the look of the bridge.

“Traffic backs up to PCH in the afternoon,” said Corby Baumgarten, who lives off Gunston Drive just south of Sunset and west of the freeway — in the thick of the action.

Complicating matters, Church Lane, which runs parallel to the freeway just to the west, has been closed to all but local traffic because of a Los Angeles Department of Water and Power project.

As a result, Acari Drive, a narrow street that curves through Brentwood Glen, “is a freeway now,” said resident Barbara Stolar. “It’s always been a shortcut. Now it’s an alternative route to Sepulveda.”

The bridge demolition is starting about a month behind schedule. Later this year, workers plan to begin demolishing the bridges at Skirball Center Drive and Mulholland Drive. The MTA and Caltrans expect the entire project to be completed in 2013. In the intervening years, construction will occur on all three bridges at the same time.

During demolition, Sunset Boulevard will be closed at night in both directions Friday through next Wednesday. Detour information and maps are available at https://www.metro.net/405.

“It is our goal to keep traffic flowing as smoothly as possible,” said Mark Van Gessel, a manager of the project. “If people could avoid the area at night, it would be beneficial.”

martha.groves@latimes.com