Shawn, Mark,
GI's told me was that the tractor/trailer "hit" something on the shoulder of the road, that caused the trailer to go all katywampass, the load shifted and slid off into the ditch...
I don't buy it,
Looks more like the driver wasn't paying attention and drove into the ditch. HET's operate on a hell of a lot rougher roads in Iraq and at very high speeds. Most of the follow on forces (4ID, 3ACR and 1AD) in 2003 came up on them with crews in place ready for contact.
I had a Super HET get goofy on one of my platoons tanks (B22) at NTC coming down Brown/Debmon pass on Barstow road in 2001. Trailer got all "Katywampass" but never shifted the load like that. The tank did not slide off but the forces were enough to break a set of trailer dolly wheels off. M106 is a lot lighter, makes me agree with Mark.
Joe D