Which device in the controlling cab shows cab signal aspects?

The Aspect Display Unit (ADU) is the correct choice as it serves a critical role in the control cab of a locomotive by indicating cab signal aspects. This device displays various aspects of the train signals, which provide essential information for the safe operation of the train, allowing conductors and engineers to understand the conditions of the track ahead.

The ADU typically presents information such as speed limits and signal statuses, enabling the crew to make informed decisions regarding train operation, especially in areas where traditional signals may be obscured or unavailable. By utilizing information from the cab signals, the ADU enhances safety by ensuring that the train operates within the prescribed limits and adheres to any operational requirements indicated by the signals.

Other devices—such as the Automatic Train Stop, which is primarily designed to enforce compliance with signals by stopping the train if the conductor fails to act; the Alerter, which reminds the operator to remain aware and alert; and the Locomotive Speed Limiter, which restricts the speed of the locomotive to prevent it from exceeding safer operational limits—each serve unique safety functions, but they do not specifically provide visual aspects of signals as the ADU does. Thus, the Aspect Display Unit is fundamentally important for conveying signal information to the train crew