In what situation would a resume speed signal be indicated?

A resume speed signal is indicated when a train that was previously operating at a reduced speed due to certain restrictions has received clearance to return to its normal speed. This typically occurs after the train has passed a particular point, such as a signal or a designated area, that permits it to resume the speed outlined in its operational parameters.

In the context of train operation, maintaining a clear understanding of speed signals is crucial for safety and efficiency. The correct indication of a resume speed signal signifies to the train crew that they can safely increase their speed back to the normal limit, which helps to maintain schedules and ensure the efficient flow of rail traffic.

The other choices relate to different scenarios where other types of signals would be relevant. For instance, approaching a stop signal would indicate the need to slow down or halt, while entering a station requires careful speed management, typically indicating a need for a reduced speed signal. A situation wherein a train is moving without any restrictions can be more generic and might not necessarily follow the specific signaling protocols that focus on indicating a return to normal speed.