When the radio is being used to control train movement, when are hand signals allowed?

In the context of train operations, specifically when using a radio to control train movement, hand signals are allowed primarily for stop signals. This is because hand signals can provide a clear, visual cue to the engineer or crew, ensuring that the message to stop is communicated effectively, especially in situations where radio communication might be compromised or for reinforcing commands.

Hand signals serve as an additional layer of safety and clarity when stopping the train, which is a critical action in rail operations to prevent accidents or unsafe situations.

While other options might seem plausible, they do not align with established procedures where hand signals are typically reserved for specific scenarios, such as signaling a stop, to maintain a clear line of communication without causing confusion. The necessity for clarity in critical commands is essential in ensuring the safety and efficiency of train operations.