A further enhancement designed to work in both signaled and dark territory is Positive Train Control, or PTC. This system is an overlay on the conventional methods of operation but also uses satellite-based tracking and computerized radio communication to verify the authority given to the train, current location of the train, the status of the next signal (if any), the position of switches (which will be equipped with a sensor and radio transmitter), and the location of any oncoming trains. As in ATC, if a dangerous situation arises, the system will apply the brakes.