Tyres also throw stones and dirt at cars behind, sometimes with remarkable force. But you're right, road debris is a serious question here. I can only imagine that this is so obvious that it cannot have been overlooked.

Surely the intake will need to be minimally filtered, my guess is something similar to fly screen mesh (screen door material, for the yanks) or finer. Debris would then just fall to the ground when the fans aren’t running.