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