Under what circumstance can a train operate against the current of traffic beyond signals?

The correct answer, which states that a train can operate against the current of traffic beyond signals by obtaining explicit permission as outlined in specific rules, is accurate because it highlights the necessity of following established protocols for safety and operational integrity in railway management.

In railway operations, specific rules are put in place to manage how trains interact with signals and other trains. Operating against traffic flow is a critical situation that can lead to dangerous outcomes if not managed properly. Therefore, explicit permissions ensure that there is clear communication and coordination among all parties involved, reducing the risk of accidents.

Obtaining permission ensures that the train crew is aware of the current conditions and any other trains that may be operating in the vicinity, allowing them to proceed with the necessary caution and awareness of potential hazards. This adheres to the principles of safe rail operations and effective traffic management.

The other options do not offer the same level of safety assurance or compliance with established protocols. For instance, clearance from the control operator without adherence to specific rules might overlook important safety considerations. Similarly, being signaled by another train lacks the comprehensive oversight a control operator provides. Operating at any time with caution, without explicit permission or procedures, disregards essential safety measures and could lead to dangerous situations on the tracks.