This....
But if you are using a safe following distance the odds of catching a rock to the windshield is pretty low. I have noticed most driver don't understand the concept of safe following distance. I had a lady call in on me because I straddled a road gator(a piece of a blown out tire) and she was too close behind me, and guess what, she couldn't straddle it. I guess it messed her Prius up pretty good.
I call BS. I've been in the other lane and had rocks hit my windshield. No one can control traffic in the other lane or vehicles changing lanes too close in front of you. I try to avoid getting near rock trucks at all costs, even if it means drastically reducing my speed. I won't even pass them in the other lane these days. I still have them come whipping past me and they frequently change lanes as if they're the only ones on the road.
I think the quarry should pay to have the roadway swept frequently. Everyone knows exactly where all that gravel is coming from.