When a train is entering a single track under Rule 251, what information must it ascertain?

The correct answer is the requirement for a train to ascertain that all opposing regular trains due that are superior have arrived or left when entering a single track under Rule 251. This rule is critical for ensuring the safety and efficiency of train operations on tracks that are only able to accommodate one train at a time in each direction.

When a train prepares to enter a single track section, it must confirm that there are no other superior trains opposing its movement that could cause a conflict. This means checking that any trains that have priority or right-of-way on that track have either completed their travels through that section or are no longer present. This safety measure helps to prevent potential collisions and ensures that the train can proceed safely.

Other considerations like weather conditions, track maintenance schedules, and distance to the next station, while important for overall train operation, are not specific requirements of Rule 251 regarding the entry onto a single track. These factors may influence operational decisions or train handling, but they do not replace the priority of ensuring safe passage by checking for opposing traffic.