The Federal Railroad Administration (FRA) sponsored Transportation Technology Center, Inc. (TTCI) to define the requirements for Interoperable Employee-In-Charge (EIC) Portable Remote Terminal (PRT) functionality for use with Positive Train Control (PTC) systems. The Interoperable EIC-PRT is a safety overlay system that integrates with PTC to protect maintenance-of-way (MOW) workers by placing the entry of trains into work zones (WZ) under the control of the EIC. This research was conducted between 2016 and 2021. Collaborating with the North American railroad industry, the team developed systems engineering documents defining the EIC PRT system, including the interoperable requirements for the EIC PRT, EIC Server and Onboard segments. Additionally, the team developed a prototype Roadway Worker Terminal (RWT) application following the interoperable requirements and tested the application to demonstrate requirement compliance.