How must a return movement be made if a portion of a train is left on a main track?

When a portion of a train is left on a main track and a return movement is necessary, it must be conducted at restricted speed. This is crucial for safety and operational integrity. Restricted speed allows the crew to have a better reaction time to any obstructions or conditions that may be present on the tracks. It ensures that the train can stop in time, allowing the crew to respond safely to unexpected situations.

Additionally, conducting the movement at restricted speed is aligned with protocols designed to safeguard not only the train involved but also other trains operating on the same track. High speeds could lead to dangerous situations if the crew encounters an obstruction or another train. Thus, returning at restricted speed is the safest and most appropriate method to follow in this scenario, prioritizing safety over efficiency.