Intelligent Railroad Systems

Nationwide Differential GPS (NDGPS) is an augmentation of the Global Positioning System (GPS) that provides 1- to 3-meter positioning accuracy to receivers capable of receiving the differential correction signal. It is an expansion of the U.S. Coast Guard's Maritime DGPS network and makes use of decommissioned U.S. Air Force Ground Wave Emergency Network (GWEN) sites to calculate and broadcast the differential correction signals. NDGPS receivers will be placed on locomotives and maintenance-of-way vehicles where they will calculate location and speed, and that information will be transmitted back to the railroad control center over the railroad's digital data link communications network. NDGPS is now operational with single-station coverage over about 80 percent of the landmass of the continental U.S., and is expected to be fully operational with dual-station coverage throughout the continental U.S. and Alaska by the end of 2004. To ensure continuity, accuracy, reliability, and integrity, NDGPS is managed and monitored 24 hours a day, 7 days a week from the Coast Guard's Navigation Center in Alexandria, Virginia. NDGPS provides a GPS integrity monitoring capability; it gives an alarm to users within 5 seconds of detecting a fault with the signal from any GPS satellite. NDGPS signals are available to any user who acquires the proper receiver,without fee.