Here's what happened: The boom of the trackhoe struck the first main beam of the bridge below the deck and handrail. As it moved throught the bridge, the boom was pulled upward and over-extended the rams which failed either in the rams or brackets holding them on. Then when the boom hit the center main beam of the bridge it stopped and tipped the trackhoe up, breaking any binders or chains that held it, and smashing the cab into the bottom of the bridge (note damage to bridge at bottom trailing edge, and trackhoe cab). The track hoe was then wedged up against the bridge and the step in the low boy trailer (this was not a flat bed as stated). The remaining momentum apparently caused the trailer to fail at the goose neck or tounge as you can see the back end of the trailer in the photo, but not the tounge. To cut throught the bridge completely, you would need bind the hoe to the trailer with something stronger and reinforce the trailer tounge to withstand the forces imposed by the bridge. But the bridge was apparently strong enough to cause 3 other components to fail first: the rams, the binders, and the trailer. The boom was the one component that looks like it could have cut through the bridge if it could have been held securly by the others that failed.