How must the Alerter be used under ATC regulations?

The correct answer reflects the importance of consistent procedures in train operations under Automatic Train Control (ATC) regulations. The Alerter system is designed to enhance safety by ensuring that train engineers remain attentive and aware of train status during operations. Under ATC, the Alerter must be used as a mandated part of the operational protocols, similar to procedures established before the implementation of ATC. This foundational approach helps maintain uniformity and minimizes the risk of accidents that could arise from varied usage patterns.

Using the Alerter in a way that aligns with pre-ATC operations ensures that all engineers are operating under the same understood conditions, reinforcing safety protocols and ensuring that the responsibilities of maintaining control and awareness throughout the journey are followed rigidly. It is not optional or solely at the discretion of the engineer, nor is it reserved only for emergencies, as those scenarios would detract from the proactive measures designed to prevent incidents in the first place.