Positive train control (PTC) is a communications-based train control system designed to prevent some serious train accidents. The Government Accountability Office (GAO) completed this report, which discusses railroads’ progress in developing PTC and the remaining steps needed to implement it, the benefits of and challenges in implementing other safety technologies, and the extent of the Federal Railroad Administration’s efforts to fulfill the PTC mandate and encourage the implementation of other technologies.
http://www.gao.gov/new.items/d11133.pdf