Communications Based Positive Train Control Systems Architecture in the USA

The implementation of railroad PTC systems in the United States has been hindered by the lack of a suitable regulatory environment. Understanding implementation efforts have often been further hindered by lack of a clear understanding of the basic PTC architecture and functionality. This paper summarizes the recent regulatory change that supports the implementation of PTC in the United States. The final regulation poses its own challenge, especially when a government agency and a regulated industry need to make a transition from prescriptive-based to performance-based standards. However, the new regulations provide positive benefits over previous prescriptive approaches in implementing PTC. This paper describes basic PTC architectures and functionality being adopted in the railroad environment, and closes by highlighting two different implementations of the same basic PTC architecture.