What must a train do when encountering a red flag or light displayed between the rails?

When a train encounters a red flag or light displayed between the rails, the correct action is to stop and not proceed until the flag or light has been removed. This signal indicates a hazardous situation or obstruction ahead, necessitating an immediate halt to ensure the safety of the train and its crew. A red flag or light serves as a warning that there could be maintenance work, equipment on the tracks, or other dangers that require the crew's attention and caution. Stopping ensures the crew can assess the situation fully and avoid potential accidents or injuries.

This precaution is crucial in maintaining safety protocols, as proceeding under such conditions could lead to severe consequences, including collisions or derailments. The requirement to wait until the obstruction is cleared before proceeding emphasizes the importance of safety and adherence to operational rules in railway contexts.