When must inferior trains clear the block of opposing regular trains?

The correct response indicates that inferior trains must clear the block of opposing regular trains in no less than five minutes. This requirement is established to ensure safe train operations, allowing sufficient time for regular trains, which have priority, to approach. The five-minute rule serves as a safety buffer, accounting for potential delays or unforeseen circumstances that may occur upon the arrival of the inferior train.

Additionally, this clear time period helps maintain the flow of train traffic and prevent conflicts on the tracks, which is critical in a busy rail network. Delaying crossing over not only upholds safety protocols but also provides crews with time to conduct necessary inspections or prepare for departure, ensuring all trains operate smoothly and safely.

In contrast, the other options would either not provide enough time for necessary precautions or could risk compromising the safety and efficiency of the rail system. The three-minute and ten-minute guidelines are not aligned with standard practices in train operations as articulated in the Operating Rule Book. By adhering to the five-minute requirement, operations can maintain regular service schedules while prioritizing the safe movement of trains within the network.