What action must a train take when encountering a signal indicating STOP AND PROCEED?

When a train encounters a signal indicating STOP AND PROCEED, the appropriate action is to stop the train and then proceed with caution. This type of signal requires the train to first halt before moving further. Once the train has stopped, the crew must then proceed while being aware of their surroundings and any possible hazards, ensuring that the movement is safe and controlled.

Choosing to continue with caution (as provided in the answer) aligns with the protocol that after stopping, the crew must observe the area ahead and proceed only when it is safe to do so. This method allows the crew to monitor any potential obstacles or signals that might affect the train's movement.

The other options, such as stopping immediately without proceeding (which is technically implied but not the complete procedure), proceeding at normal speed without caution, or following a prior indication without reassessing the situation, do not comply with the nuances of the STOP AND PROCEED signal's requirements. Understanding the specific steps of stopping and then cautiously proceeding is essential for ensuring safety on the tracks.