What does the APPROACH RESTRICTING aspect consist of?

The APPROACH RESTRICTING aspect is represented by the signal combinations that indicate an upcoming condition where the train must be prepared to stop or proceed at restricted speed. The correct configuration for this aspect—solid yellow over lunar or solid yellow over lunar over solid red—clearly indicates that the train is approaching a signal that restricts its movement and may require it to prepare for a slower speed or stop.

The solid yellow light signals the train to approach with caution, while the lunar light or additional solid red provides further context about what to expect ahead. The dual nature of the lights (one indicating caution and the other signaling the potential need to stop) is crucial for ensuring that train crews have adequate warning to react safely as they approach signals that might be displaying more restrictive aspects.

Understanding the significance of these signal aspects is essential for ensuring both the safety of railway operations and adherence to operational protocols. The other options do not accurately reflect the characteristics of the APPROACH RESTRICTING aspect, as they specify different combinations that are seen in other signal states.