Something else to worry about too though, is the people in vehicles that will throw things at you.
It is a different breed of people out there, for whatever reason, although I have some answers as to why....
But riding that far, if that road is as busy as I am remembering? No way I would try it.
Do you not have a truck and trailer of your own, or can you not borrow one? That would be far cheaper even buying one, than any vet/medical bills that you and your horse could incur.
Even years ago, and this was in 60's? I have even been riding in pasture, and been close enough to road that horse was hit by pop bottle thrown at us.
And as for the delivery truck, can't remember who posted that, BUT, if you even know the name of the company? Call them and report this, even now, as they will more than likely have drivers on set runs, or have the system that will tell them EXACTLY what driver did that, as the system shows where driver was and what time. But call them.