What must not be changed until it is known that a reverse movement has been completed?

The reason why the route must not be changed until it is known that a reverse movement has been completed is rooted in safety and operational protocols. When a train is reversing, it is crucial to maintain the established route to ensure that all movements are accounted for and that no unexpected conflicts arise with other trains or track systems.

Changing the route prematurely could lead to miscommunication and unsafe conditions, especially if the reverse movement requires specific track alignments or protections that are only valid for the original route. Until the completion of the reverse movement is confirmed, altering the planned route could jeopardize the safety of the train and any surrounding rail operations.

In contrast, aspects such as the radio communication device, engine type, and train schedule are elements that can be adjusted or confirmed independently of the reversal process, as they do not directly affect the safety and integrity of the movement on the tracks. Thus, the emphasis on maintaining the route until the reverse movement is finalized serves to uphold safety and coordinate train operations effectively.