A dark signal with no aspect indicates what action for a train?

A dark signal with no aspect indicates to a train that it must stop. This condition signifies that there is either a signal malfunction or that the track is not clear for movement. In rail operations, signals are critical for maintaining safe distances between trains and ensuring that they proceed only when it is safe to do so. A dark signal is interpreted as a cautionary signal that the train cannot proceed, and stopping is the immediate and necessary action.

The importance of stopping at a dark signal is underscored by safety protocols designed to prevent collisions or accidents on the track. This is a fundamental rule in train operations, emphasizing the need for vigilance and adherence to signals, especially when signals are not displaying clear instructions.