What must happen when a red flag or red light is displayed?

When a red flag or red light is displayed, it signifies that a train must stop unless instructed otherwise. This response is critical for ensuring the safety of train operations. The display of a red signal indicates a hazardous condition or an obstruction on the track, requiring immediate attention. Stopping allows train crews to assess the situation, communicate with dispatch or control personnel, and determine the next course of action.

Proceeding without stopping or slowing down could result in accidents or collisions, making it crucial for crews to adhere to the directive of stopping when faced with a red signal. The importance of this rule is underscored in railroad operations, which prioritize safety and communication above all else.