How can a bridge sustain its own weight and the weight of a truck if I've blown out the load-bearing supports underneath it?
Try for yourself; put a bomb on each leg of the bridge on the underside and then put the third one on the middle pole above the bridge. *KABOOM* The bridge holds like nothing happened to it and a semi-truck manages to roll right over it without any problem.
Terrible game, terrible first level, terrible design.