I know that curve by the tree farm and horse ranch. It is deceiving and you don't realize how sharp it is until your in it.
I've been on that road during the week when Claytons is in operation and yes those trucks hall ass full and empty. I admit to doing 55-60 on the straights and quite often I have one of those trucks on my ass that "came out of nowhere".
To my knowledge these are all independent operators and yes they are paid by the load. There are 2 sand pits side by side but Clayton is the most active. I assume this is who the trucker was hauling for. Clayton is by no means "questionable".
The report says he was hauling cement. I don't see cement in the photos but sand for cement. I don't believe there is cement [dry] making facilities at the sand pit, but could be wrong.