During the Loma Prieta earthquake in 1989. It took months to fix the bridge and the traffic was a nightmare during that time. Even at the best of times the traffic is horrific during commute hours. People started using the ferries again and BART which is the rapid transit train. BART runs under water under the Bay Bridge but it was OK after the earthquake.
I'll never forget how all the TV stations and businesses came together to figure out a way for people to get to work again. Working hours were staggered. Businesses called the tv and radio stations to put out news about working hours, alternate routes, carpools, etc.
It was amazing to watch our local anchors rallying for the Bay Area. It went on for days, because every freeway has dozens of overpasses which had to be checked out before cars were allowed to drive on the freeways under them or on the overpasses. Then they had all those people sandwiched between the lower and upper deck of a half mile of freeway going through Oakland. Some of the people survived, but many were crushed to death.
It happened just as the baseball game between the Oakland As and SF Giants was starting so most of the people were at the game or had gone home early to watch the game. Lucky that the freeways were so empty. As bad as it was it could have been so much worse.