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Any rail safety system that relies on humans can fail and cause a crash, says
Westinghouse Air Brake of Wilmerding, Philadelphia. The only foolproof system,
it says, is for all trains to have a Global Positioning System satellite
receiver which continually monitors the train’s position (WO 99/52091). This
information, along with the train’s speed and travel direction, is transmitted
by radio to all other trains in the area. Each train builds a continually
changing map of the relative positions of the other trains. Whenever a
potentially dangerous situation arises, both trains transmit warning signals to
the respective crews. If these are ignored, a further signal applies the
brakes.