What is required for a train to pass a red flag according to track bulletins?

For a train to pass a red flag, it is essential that it receives explicit permission from the employee in charge. This protocol is in place as the red flag serves as a warning indicator that there are specific conditions or hazards present on the track, such as maintenance work or an obstruction. The requirement for explicit permission ensures that the safety and integrity of both the train crews and any workers on or near the track are maintained. It allows the employee in charge to assess the situation, communicate any necessary precautions, and provide instructions to ensure that the train can safely proceed past the warning. This practice aligns with safety regulations and procedures designed to prevent accidents and ensure streamlined operations in potentially hazardous situations.

The other options do not fulfill the necessary safety protocols outlined in track bulletins regarding passing a red flag.