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