When should a train must be clear when instructed to do so by the dispatcher?

A train must clear the track as instructed by the dispatcher before the following train receives a restrictive signal because this ensures the safe movement of trains on the same line. The dispatcher is responsible for managing train movements and must maintain safe distances between trains to prevent collisions. When a following train receives a restrictive signal, it indicates that it must reduce speed or stop. By having the preceding train clear before this occurs, it creates a buffer and allows the following train to proceed safely without the risk of encountering an occupied track.

This understanding of train signaling and the dispatcher's role is crucial in maintaining operational safety and efficiency.