The driver realized that back trailer was a couple inches too tall to get under the overpass empty so he tipped it to get under there! Then there is a nice bridge I have for sale... That's one of those that after it is over with even people that don't think they are religious look up to the sky afterwards and say, "Thank you Lord!"
Trucker may not even known it happened until the bounce. Not uncommon with joints, but that was extreme. One reason lightest trailer always goes in back, even if it requires uncouple and recouple.