What is a key indication of a malfunctioning ATC system?

A key indication of a malfunctioning Automatic Train Control (ATC) system is the complete failure of ATC car-borne equipment. This system plays a crucial role in maintaining safe train operations by monitoring and controlling train speeds and ensuring adherence to signal indications. When there is a complete failure of the equipment that comprises the ATC, it means that the entire system is incapable of performing its vital functions such as speed regulation and signal enforcement.

While other signs, such as unexpected speed increases or frequent signal changes, can suggest issues with the system or the overall operation, they do not indicate a total breakdown. These conditions may arise due to various factors, such as human error or temporary malfunctions, and may still allow some operation of the ATC system. In contrast, the complete failure of ATC equipment would likely render trains unable to operate safely or could halt operations entirely, indicating a more severe issue that needs immediate attention.