The unloading station includes a door moving mechanism for moving the doors of the vehicle to {HEAD ~ the open position} upon {TAIL ~ its arrival} at the station 
upon
The unloading station includes a door moving mechanism for moving the doors of the vehicle to { HEAD ~ the open position } upon { TAIL ~ its arrival } at the station
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH