In 1989, the SF Bay Bridge suffered a collapsed section which shut down all traffic for 3 months. That's why I drove my co-workers to the Marina; their homes were across the Bay in Oakland and they couldn't easily get home, so I drove them to relatives in SF. Traffic was snarled. All electricity was out for the greater part of a week. Electric trolley buses and light rail were stuck in the streets, no traffic signals were operating, BART was shut down indefinitely after the quake struck. There were masses of people downtown walking in the middle of streets trying to find a way home. All this from one bridge shutting down.
When the big one hits, I fear that several bridges across SF Bay will shut down. CalTrans has been retro-fitting the bridges since 1989. However, there were several scandals about sub-standard concrete and iron being used from suppliers (Chinese, mostly). Decisions were made to continue with the retro-fitting since the materials were embedded and it would be too costly to start over. The SF/Oakland Bay Bridge retro-fit won't be completed for another 5 years.
We're overdue for a big quake on the Hayward fault which has the potential for being 7.0 to 8.0, not to mention the possibility of the San Andreas fault snapping on the SF peninsula with a 7.0 or greater quake soon.
We are overdue here in LA in several areas. We have the Ft Tejon/San Andreas which the last one was 150 years ago and we have a fault running right underneath Downtown LA that has bot moved on over 200 years. That scientists say is our “big one” and expected to do more damage than the one on the San Andreas Fault. Los Angeles moving north-north east at 1/4 an acre is not helping things one bit.