This is a nightmare scenario. A wheel comes off a truck or something and keeps rolling down the highway at full speed. Obviously since nothing is controlling the direction it's going in, this wheels is basically a cannonball bound to come into contact with something. The worst thing that could happen is it goes on the other side of the freeway, and that's exactly what happens. After crossing the median barrier, the wheel misses a few cars and then BLAM... hits a vehicle and basically destroys it. I hope whoever was in that vehicle did not suffer any serious injuries. Whether they did or not I would be scared as hell to ever drive on the highway again.