That beam they took out is called a "sacrificial beam." It was not a structural support, but was meant to take the impact before any structural members were damaged. You'll see them on many modern bridges and underpasses.
That's interesting and seems like a good idea, except perhaps it should be paramount that the 20-ton beam NOT fall on the following cars! That is an entirely different meaning of "sacrificial"...
See the videos on 11foot8.com, that beam is a freestanding structure separate from the bridge solely designed to decapitate trucks.
The sacrificial beam that appeared to fall on top of the car behind the truck?