In the closed position, the doors constitute {HEAD ~ side walls} to prevent {TAIL ~ removal} of the freight from the vehicle 
to prevent
In the closed position , the doors constitute { HEAD ~ side walls } to prevent { TAIL ~ removal } of the freight from the vehicle
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH