When I was twenty, and living in MIami, I was following behind a 10 wheel dump truck on I95.
I was about to pass him when I noticed a large white object stuck between the two left rear tires going round, and round. Just as I realized it was a mellon sized stone, it flew straight out, and right at me.
I ducked, and swerved to the right, and heard that VVVVVVVVVV sound as that rock flew about 6 inches to my left. Right at head level.
I stay away from trucks period.