so that {HEAD ~ particulate material} placed in the hopper truck may be spread in a uniform layer on {TAIL ~ a road surface} over a predetermined path width 
spread on
so that { HEAD ~ particulate material } placed in the hopper truck may be spread in a uniform layer on { TAIL ~ a road surface } over a predetermined path width
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH REL OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH