No. PTC is more than GPS. Much more than that: 1) which track is the train on? GPS off by a few meters 1 way or the other means a different track. 2) What ar

No. PTC is more than GPS. Much more than that: 1) which track is the train on? GPS off by a few meters 1 way or the other means a different track. 2) What are the switch settings ahead? 3) Is there a train stopped ahead? 4) Is there any obstruction ( i.e. rock fall )? 5) Are the crossing gates ahead properly functioning? 6) Are there vehicles across the crossing ahead? 7) What are the normal speed restrictions in place? 8) Are there maintenance workers ahead? 9) Are there temporary speed restrictions in place because of tracks needing repair? 10) What is the mass of the train? Heavier trains = greater stopping distance. 11) What is the track surface - leaves in the fall can create a biofilm that increases stopping distance. 12) What is the cargo - some cargo requires more gradual deceleration - bottles of wine anyone? 13) What about tunnels? 14) What about mountainous terrain with poor line of sight to GPS satellites? 15) What about signals that may interfere with a GPS fix? 16) What about going through cities with buildings and in trenches? Expanding on a few additional points: "Where is the train in front of this train"? a) Its not enough to know where the locomotive is: some freight trains can be 2 miles long. So if the train in front is 2 miles ahead but is a passenger train - no problem. A freight train? Big problem. b) Is the train ahead on a siding that the current train will not hit because the switch is thrown to transfer to another track? "What is the allowed speed?" a) Is the train going to take a speed restricted curve? b) Or continuing straight at a higher speed? c) How fast can the train decelerate - freight is slower than passenger trains. In a car its annoying -but having a train get confused and go into an emergency stop - that is something else. This is not a simple problem. Then throw in all the systems that need to interact and function correctly, have good failsafes, etc. There is a reason why trains need humans driving them!