Which signal aspect would require a train to stop the operation and stay at that signal?

The signal aspect that necessitates a train to stop and remain at that signal is the stop and stay signal. This signal indicates that the train must come to a complete stop and cannot proceed until the signal changes to a more favorable aspect. It serves as a crucial safety measure, ensuring that the train does not move until it is appropriately cleared to do so.

Clear signals provide guidance for the train to proceed without restrictions, while proceed with caution signals indicate that the train should continue but be prepared to stop for any potential hazards ahead. Reduced speed signals instruct the train to decrease its speed as a precaution, yet they still allow for continued movement. In contrast, the stop and stay signal unequivocally requires the operator to halt and wait, emphasizing the importance of these signals in maintaining safe train movements and operations.