a second positioning system arranged in {HEAD ~ the second vehicle} for determining {TAIL ~ the position} of the second vehicle; and 
a second positioning system arranged in { HEAD ~ the second vehicle } for determining { TAIL ~ the position } of the second vehicle ; and
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH