Oil tankers from the middle east go under the Golden Gate all the time. If one was head full speed into a support or explode under the bridge ? Sounds a lot like the MOA for 9-11.
How do you stop a tanker? Blow it up and the bay will be full of oil,which would also be very damaging.
All commercial traffic must give 96 hours notice that they are coming into port. They are meet at the sea buoy (the twelve mile mark) and along with the Port Pilot two armed Coasties board. They inspect the papers and the crew and protect the pilot whilst he brings the ship under the Gate.