@pointysticksncoffee as a child I remember being impressed by tank traps - even something as powerful as a tank could be stopped by a simple change in levels. What you are describing seems to be a wheelchair trap - designed to prevent access. To be more efficient, the lower floor (which could be even lower) should be a soft surface to ensure that the wheelchair tips up at this point. Only a short section of soft, of course, because we want the occupant's face to make contact with