This is particularly useful when {HEAD ~ the first and second mobile users} are traveling in {TAIL ~ respective cars} or other vehicles 
are traveling in
This is particularly useful when { HEAD ~ the first and second mobile users } are traveling in { TAIL ~ respective cars } or other vehicles
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH