Doors or gates are provided to control the amount and width of {HEAD ~ the discharge} of particulate material to {TAIL ~ the highway surface} 
Doors or gates are provided to control the amount and width of { HEAD ~ the discharge } of particulate material to { TAIL ~ the highway surface }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL