proposes an autonomous train control system based on inter-train communication. In this new system, there is no logical central device and trains can communicate with each other autonomously. The train itself produces the position and calculates the permitted track speed. Therefore, the distance between trains can be shortened and a smooth brake pattern can be obtained. For building this system without hindering the current system operations, the gateway-based replacement technology and its test methods are explained. The assurance of test methods has been evaluated by comparing the on-line/off-line properties of the proposed technology