The seismic solution was the outright replacement of Doyle Drive, but it's roughly the same age as the Golden Gate Bridge. And, after the Loma Prieta earthquake, engineers concluded that the bridge might collapse in a magnitude 7 or greater earthquake. Serious consideration was actually given to replacing the bridge, but retrofitting was found to be more cost effective.
There have been many technological advances since the Golden Gate Bridge opened in 1937. Still, Bridge District Chief Engineer Ewa Bauer says though there was less know-how about how to engineer for seismic safety, there was one thing they did very well. "It was decided yeah, we better make sure it can take a strong wind because that was something people had a better knowledge of," she said.
In 1982, high winds shut down the Golden Gate Bridge, which was designed to move up and down 16 feet, left to right 27 feet, in those conditions. Right now, it could handle winds up to 68 miles per hour and there are improvements coming to make it withstand 100 miles per hour. Seismic upgrades have been added continuously since 1997 and won't be finished until 2018.
How long will the bridge last? Bauer can't imagine ever replacing it. "What we are doing now, we are simply repairing small elements or large elements that need replacement, but you can truly do it indefinitely," she said. Doyle Drive, humble appendage to the bridge, is getting a major facelift and seismic retrofit that will take it from the bottom seismic rating to the top. Final preparations are underway for this coming weekend's closure and then re-opening as a whole new route on Monday.
While the bridge has to meet the highest seismic standards as what's called a "lifeline structure," Doyle is a notch below, classified as a "recovery facility." "If there is a high-magnitude earthquake, there are other ways to get from Point A to Point B," said Dave Pang with Caltrans.
Come Monday, there will be no cars on the old elevated section of Doyle Drive. Both north and southbound traffic will be driving on a shiny new viaduct leading into a new tunnel which will be part of a three-year detour. Doyle Drive will be closed from 8 a.m. Friday to 5 a.m. Monday. Caltrans advises drivers to avoid the area if at all possible.
How you will get around the Doyle Drive closure? For more information on the traffic impact and alternate routes, check out ABC7 News' exclusive Waze traffic app.