alder:
The height of that bridge is known, it is 13’ 9" and taking that image into photoshop rotation and measuring I roughly make that trailer to be 14’ 2" so 5" approx. hit the bridge 
Its a 40 ft High Cube, they run at about 14’ 6" (The box is 9’ 6" and the skel is about 5’ depending on 5th wheel height)
Maybe he mistook it for a normal 40 footer, which is 1’ shorter.
I don’t think the bridge was closed, National Rail normally don’t close (or at least not for very long) a bridge with a reinforcement bar on, which this one clearly has
When I pull containers they are either 13’6 or 14’6 (standard or high cube) so its quite possible he just forgot he had a high cube. Our units are always set for 14’6 though so they cant really go wrong if they stick to that
Some of the comments on the link were comical. His mate said he was 13’ 9", people talking about low ride heights etc, arguing about the size of the box. I’ve done containers long enough to know the driver ■■■■■■ up. It happens, all you need to do is hold your hands up and say you got it wrong. We’re all human, but there’s nothing worse than trying to squirm off the hook by trying to blag people that know better. Nothing worse than standing next to your handy work, trying to insult people’s intelligence