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