What must be communicated to trains regarding the interlocking when using Rule 280A?

When utilizing Rule 280A, it is essential to communicate the specific interlocking where this rule will be displayed to the trains involved. This ensures that the train crews are aware of the precise location where they need to be attentive to the protection methods in place during the interlocking's operation. By clearly identifying the interlocking location, crews can prepare appropriately for any changes in operations, signaling, or track status that may impact safe control of the train. Effective communication of this detail is crucial for maintaining safety and operational integrity in the railroad environment.

The other options, while important in a broader railroad context, do not specifically pertain to the requirements under Rule 280A as directly as the interlocking location does.