The control center knows at {HEAD ~ any time} by {TAIL ~ radio contact} where the train is traveling 
The control center knows at { HEAD ~ any time } by { TAIL ~ radio contact } where the train is traveling
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH