Overview
The main concept in PTC (as defined for North American Class I freight railroads) is that the train receives information about its location and where it is allowed to safely travel, also known as movement authorities. Equipment on board the train then enforces this, preventing unsafe movement. PTC systems may work in either dark territory or signaled territory and may use GPS navigation to track train movements. The Federal Railroad Administration has listed among its goals, "To deploy the Nationwide Differential Global Positioning System (NDGPS) as a nationwide, uniform, and continuous positioning system, suitable for train control."
Various other benefits are sometimes associated with PTC such as increased fuel efficiency or locomotive diagnostics; however, these are benefits that can be achieved by having a wireless data system to transmit the information, whether it be for PTC or other applications.
In the 1990s, Union Pacific Railroad had a partnership project with General Electric to implement a similar system known as "Precision Train Control." This system would have involved moving block operation, which adjusts a "safe zone" around a train based on its speed and location. The similar abbreviations have sometimes caused confusion over the definition of the technology. GE later abandoned the Precision Train Control platform.
Read more about this topic: Positive Train Control