Probably a tri-axle dump, they need that axle down to meet weight restrictions on so many pounds per axle. But you need to lift it to make sharp turns, otherwise you scrub that axle sideways (it’s usually the first of three rears) as the truck fights to go straight. Sometimes driver forgets to put it back down after turn (has to be back down in specified distance from turn).
Thanks, that’s kind of what I thought. I never see them down. You mean, a driver somehow has to anticipate a sharp turn in the road (or I guess there is a map notation) and pick them up, then drop them when the road becomes straighter?