The last picture showed the tractor a couple hundred yards from the trailer. Pretty small in the picture.
I doubt that loading that machine backwards would have made much difference. The boom travelling at say 50 MPH hitting that bridge, and even wedging itself underneath would have likely lifted the bridge off its foundations. Yes, it probably wouldn't have punched thru the deck, but still caused million's of dollars worth of damage.
A trucker hauling an overheight ATCO building hit a bridge here, and although it just ripped the roof off the building, it damaged the first "T" section of the bridge so much that the section it had to be replaced.
Eagle River Bridge Damage