Very doubtful a rock would fly off truck straight onto your windshield. Im not a law finding genius, but as I recall, if a rock falls from the truck and hits the roadway before it bounces up and hits your windshield, it is considered litter or something. Our friendly lesislators protect the gravel haulers just like they allow the cane haulers to track mud onto the highways and drop cane everywhere, buy it is not considered littering.
A few years back I was heading south down I-59 and an gravel truck pulled onto the right lane ahead of me, hit a bump and ROCKS came flying out of the truck and peppered my grill, hood & roof. Rocks hit my windshield each making
3 cracks. I tried to pass him and get a name off of the door as the licsense was covered up. He hit another bump and more rocks came flying out. So I slowed down and watched several cars trying to pass him get peppered. I called LSP and gave them a description and the exit he took. I had to get to work so I couldn't follow him. My insurance paid a few hundred to repair dents in the roof, hood and replace the grill and windshield.