What happens if only one indication is possible from a signal?

When only one indication is possible from a signal, that indication governs the actions of the train. This means that the train crew is required to follow the specific instruction provided by the signal, which could indicate whether to stop, proceed, or take another action based on the context.

The reason this is significant in railroad operations is that signals are designed to convey critical information about track conditions, potential hazards, and the movement of other trains. When only one indication is available, it eliminates ambiguity, ensuring that train crews can make informed decisions and act accordingly to maintain safety and compliance with operational standards.

In this context, the other options are not applicable because they do not reflect the protocols regarding signals. For instance, stopping the train or ignoring the indication would disrupt operations and could lead to unsafe conditions. Allowing trains to proceed at any speed without regard to the signal could similarly create risks. Thus, the protocol is clear: when only one indication is possible, that indication must be followed as it governs the appropriate action to take.