What governs extra trains concerning opposing extra trains in single track 251?

The correct choice is train order because it is the method specified in the operating rules for managing the movement of extra trains on single track, particularly where opposing movements can occur. Train orders provide the necessary authority and instructions that must be adhered to for safe operations. They indicate the rights of way and any constraints or directives relevant to both extra trains, ensuring that they do not operate at the same time on the same track in opposing directions.

The use of train orders is essential in creating a clear communication protocol, as they are issued by the dispatcher to coordinate operations, particularly in scenarios where the track is limited and additional care must be taken to prevent conflicts. This method ensures that all crew members involved are aware of the current train movements and any scheduled changes or priorities, ultimately leading to safer train operations.

In contrast, automatic signals primarily manage train movements along tracks with signal indications but do not specifically govern the interactions between extra trains, particularly on single track systems. Verbal authorization could be used in certain situations but lacks the formal structure and traceability that comes with written train orders, making it less reliable for managing these opposing movements. Dispatcher instructions might guide overall operations but are not the governing authority for the specific interaction between extra trains.