Courtesy: Caltrans

A new east span of the Bay Bridge is being built alongside the old east span, which is 75 years old and slated for removal

The seismic upgrade of the Bay Bridge, California’s biggest and most complicated highway construction project, will cost taxpayers more than $6 billion and has taxed drivers with a series of bridge closings. Next weekend Caltrans, the California Department of Transportation, is once again asking many of the 280,000 drivers who traverse the bridge each day to find another way across the bay.

Appropriate to the tech-savvy population of commuters, Caltrans is asking Bay Area residents to help spread the word on blogs, local Web sites and Facebook pages. The agency has created a series of plug-in banners for commuters to embed on their favorite online sites. It has also created an online animated simulator to help explain the changes.

The agency has spent about $500,000 to spread the word via more conventional advertisements, public service announcements and fliers, along with its 300 changeable message signs throughout the state.

Unless weather delays the planned President’s Day weekend closing, it will be the second-to-last bridge interruption before the new span opens in late 2013.

Westbound lanes to San Francisco will be closed from 8 p.m. on Friday until 5 a.m. on Tuesday, Feb. 21, so that construction crews can demolish part of the old bridge and begin building the approach to the new span. Eastbound traffic will not be affected. After the closing, there will be what Caltrans calls “a slight detour” after the toll plaza.

Though Caltrans has gone to great lengths to warn drivers before each bridge shutdown, it has sometimes had trouble preparing commuters for the changes once the roadway reopens.

During work to strengthen the western span against earthquakes in the mid-2000s, Caltrans tried closing single lanes and bridge entrances, but found that caused hourlong tie-ups.

“People would line up like lemmings,” said Bart Ney, a Caltrans spokesman.

So when the agency needed to replace a milelong stretch of road on the San Francisco side of the bridge in 2006, it closed the entire lower deck for the first time and began using large-scale outreach, including an animated simulation, to warn drivers.

The techniques are not fail-proof. After a Labor Day weekend closing in 2009, drivers had trouble getting used to a detour, known as the S-curve, on the upper deck. One trucker missed the turn, drove off the bridge and was killed.

For last year’s shutdowns over the Memorial Day weekend, Caltrans devised an interactive game to reach a “younger, more tech-based group of folks” who use the bridge at night to go to bars and restaurants.

We had to “get the message where they live,” Ney said. “They live in the app store.”

The game was downloaded more than 10,000 times, he said.

This article also appears in the Bay Area edition of The New York Times.