Which action should a locomotive engineer take when a stop signal is encountered?

When a locomotive engineer encounters a stop signal, the correct and necessary action is to stop the train immediately. This protocol is critical for maintaining safety on the rail network. A stop signal indicates that the train must halt due to potential hazards or operational commands ahead. Ignoring this signal by continuing at the same speed or accelerating would pose significant safety risks, potentially leading to collisions or unsafe situations on the tracks.

Stopping immediately allows the engineer to assess the situation, communicate with control centers, and determine the appropriate next steps before proceeding. Alerting passengers with the horn is not a standard procedure when a stop signal is encountered, as it does not align with the immediate actions required to ensure safety in such scenarios. Thus, stopping the train is the correct response to comply with safety regulations and ensure the safety of the crew, passengers, and other trains on the network.