Elaborate on head on. Head on into a brick wall, or a Volvo taking a head on with a large SUV. If it were the latter the SUV would destroy the Volvo. It comes down to simple mass. Most fatal crashes are not caused by passenger intrusion though. Usually it’s something like inter cranial pressure from trauma, or a transected/ruptured aorta, or so on. If its a head on with a wall or tree mass has almost no effect on the out come, as your assumeing that the wall is imovable