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