It is the responsibility of the truck driver to secure her or his cargo. That especially goes for those who haul gravel and dirt. What you are finding is lax enforcement that leads to drivers being lazy and not tarping the cargo area.
If you are talking about debris that gets kicked up by the tires from the road, it is the responsibility of the state or local government to keep the roads free of debris.
If you encounter a truck with unsecured cargo, you have two choices. You can call your state troopers from your cell phone (in Florida it is *FHP), and report the truck. The other option is to report it to your state’s Department of Transportation. Of course, in either case, you will first need the truck number or a license plate number, which isn’t always easy to find.
The best thing to do when you encounter a truck with unsecured cargo is to keep your distance. That kind of debris usually does the most damage to vehicles immediately behind it.