What must a train do if it encounters a stop signal while operating?

When a train encounters a stop signal, it is required to contact the Block Operator for permission to pass the signal. This is crucial for maintaining safety and order on the rail system. The stop signal indicates that there is a potentially hazardous condition ahead, such as another train occupying the track or maintenance work in progress.

By contacting the Block Operator, the train crew ensures that they receive proper authorization before proceeding past the signal. This communication is essential for confirming that the track is clear and safe for the train to move forward. The Block Operator has the responsibility to manage train movements and ensure the safety of all trains operating in the area.

Other choices lack the necessary safety considerations required in this scenario. For example, continuing with caution could lead to unsafe situations if the track is not safe. Waiting for another train to clear does not address the need for authorization from the Block Operator, which is critical in maintaining safety protocols. Reversing operations immediately is not standard procedure and could create further complications or hazards without prior clearance.