Research Results: Interoperable Communications-Based Signaling as a Basis for Positive Train Control [open pdf - 154KB]
"This project demonstrated that the major suppliers of signaling equipment for the North American railroads could modify their existing safety-critical equipment to support operation of a vital interoperable positive train control system based on signaling principles developed over many decades. Project participants included the major suppliers of signal and train control equipment within North America. These suppliers have provided a wide variety of signaling equipment, including processor-based equipment that has been in revenue service on railroads and transit properties for decades. This includes equipment designed and built to the vital (or fail-safe) requirements of rail and transit properties. The project was sponsored by the Federal Railroad Administration's (FRA) Office of Railroad Development and coordinated through the Railroad Research Foundation."
U.S. Department of Transportation - Federal Railroad Association (FRA): https://www.fra.dot.gov