jump in and put the levelers on the ground! rotate the boom and turn the wheels! drop the cable and run over it then brake! There's a bunch of things they could have done.

yeah drop the outriggers, even if they were manual

All those actions may have slowed down that tonnage in motion but not once the momentum had reached a certain point. Once she got going, the combination of everything EXCEPT using the boom to stop it wouldn't have mattered. That driver saw his out with the low bridge and saved someone's home or business.

I'm going with dropping the outriggers too. I can only assume that there was something wrong with them as it seems an obvious thing to try.

Easy to say in hindsight though, that thing was really terrifying! There was just a sort of inevitability to it, like nothing was going to stop it at all.

Runaway crane, never coming back...

Wrong way on a one-way track

Oh like jamming it under a railway bridge was his rescue plan!!!???

What! That lumber didn't stop it? Here, here's another that's smaller, maybe it will work!