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