This contract examined the feasibility of a GPS system for the precise location of railroad maintenance-of-way vehicles and equipment, both on and adjacent to the tracks. Such a system would have the potential to accurately identify and communicate the precise location of on-track maintenance equipment, off-track equipment such as construction equipment, and the location of small track maintenance gangs. Such accurate and timely data would enable dispatchers to more efficiently and safely manage train traffic through locations where track operations are underway. The proposed GPS location system uses dual-frequency GPS receivers, broadcast measurements from a GPS reference station network, and dead reckoning sensors when GPS coverage is interrupted. The design objective was a system that could determine the location of on-track maintenance vehicles with a confidence level of 0.99999 when GPS coverage is available. When multiple measurements over a one minute period are combined, a confidence level of 0.9999999 (seven nines) is achieved. This accuracy enables operation where the distance between track centers is as small as 11.5 ft. The system architecture includes a GPS receiver, a receiver for broadcasts from the High Accuracy National Differential GPS network, an axial accelerometer and heading rate sensor, and carrier phase position and parallel track resolution algorithms. The project focus was primarily on the development of a key major system algorithm, the Kinematic Carrier Phase Position Algorithm, and testing of this algorithm using archived NDGPS data. Tasks included the design of detailed software and hardware architecture; the selection key system components including GPS receivers, accelerometers, and rate sensors; and the evaluation of candidate GPS kinematic phase positioning algorithms to determine which one is most suitable for this application. The Carrier Differential GPS (CDGPS) used in this study was not able to achieve the required position accuracy of 0.4 meters necessary for operation in Positive Train Control (PTC) territory. The primary limitation is satellite orbit accuracy (position and velocity). The algorithm successfully separated multipath errors from measurements, however. The results were sufficiently promising to encourage future development of this concept.
The final report for this IDEA project can be found at:
