Which operational guideline must be followed every time a train stops?

The guideline that states the ATC (Automatic Train Control) start button must be pressed every time a train stops is vital for ensuring that the train's safety systems are activated and functioning properly. By pressing the start button, the train operator re-establishes the system's oversight following a stop, ensuring the proper monitoring and control mechanisms are in place before the train resumes its journey. This action is fundamental in maintaining the safe and efficient operation of the train, as it confirms that the train is ready for movement under the oversight of the ATC system, which is designed to prevent incidents such as collisions or derailments.

The other options revolve around operational checks and communication that can vary based on specific situations or systems in place but do not directly pertain to the crucial restart of the ATC system following a stop. For instance, while resetting the alerter and checking emergency systems are important for overall safety, they are not specifically mandated to occur every time a train stops as part of the operational guidelines. Effective communication with other crews is also essential for coordination during train operations but may not be necessary at every stop, depending on the situation. Hence, pressing the ATC start button is the specific procedural requirement that must be consistently adhered to upon stopping for safety