Relax, it won't happen here in the SF Bay Area. After the 1989 quake when the Bay Bridge got knocked out, there was no panic. Major streets jammed with stuck electric trolleys and cars, lots of people walking in the streets, no electric street signals. I was in downtown San Francisco, lots of my co-workers were stranded from getting home across the bay. I drove one co-worker to her sister's home in the Marina where the fires were raging. People were calm and very mannerly. I couldn't believe how nice everyone was to each other.
Our bridges are very sturdy, and have been hit by jet planes without damage. I doubt very much that one could be damaged by terrorists, let alone several. The authorities are watching the bridges.
What if they did ALL of them at the same time?
I actually worry about this.