I was in San Francisco last Summer, so of course I had to do the tourist do-dah and visit the Golden Gate bridge. Dropping the bridge in a terrorist attack would be very difficult. However, a semi loaded with explosives could kill a lot of people during rush hour, especially if it were detonated in a tunnel. When we arrived, I was driving into the city so I wasn't looking around very much. However, I'm pretty sure we drove through a tunnel as we approached the toll booths on the south side of the bridge.

While they'd have a hard time dropping the whole bridge, they could do a lot of damage to it. If they wanted to drop a part of the bridge, they could use a demolitions technique known as tamping to direct most of the blast downward. A semi could carry about 15-20 tons of explosives with several more tons of tamping material on top. That might be enough to blow a hole through the bottom of a span and put the bridge out of commission for some time. If they managed to severely damage some of the vertical support wires, the delay could be a lot longer. According to the bridge tour, each of those support wires was made to a very precise specification back in the 1930s. The repair crews would have to dig up those specs and find a modern contractor capable of duplicating the work.

If terrorists wanted to do a lot of damage to a city, detonating a truck bomb in a tunnel is a good way to go. Last Summer, there was a major fire back East in an underground tunnel that took many days to extinguish. A big explosive in a confided space is a good formula for killing a lot of people. If you damage some bridges and tunnels going into and out of a major city like New York, Boston, or San Francisco, you could have a very serious economic and psychological impact.

At first, I hesitated to write about this stuff. I'd hate to think I was giving anyone any ideas. However, terrorists already know all of this and more.