One would think, even if that were just a plain old unavoidable failure
(picked up a spike etc.) that the driver would have pulled off to the
side of the road after he'd got it down to a reasonable speed.

It almost looks to me like the LF brake lost air pressure and locked
down only that wheel and he just slammed on the brakes to keep it from
rotating around.  Only thing that makes me question that theory is that
the truck does roll slightly after coming almost to a complete stop.
Basically, I dunno - just guessing here.  And of course the following
driver didn't even have a car next to him, just wasn't paying attention.

nate