What is the function of the horn on a locomotive?

The horn on a locomotive serves a critical safety function by alerting people and vehicles of the train's approach. This warning signal is crucial in preventing accidents at crossings and other areas where the train may be coming into close proximity with pedestrians or road traffic. The sound of the horn is a standardized way for the locomotive engineer to communicate the presence of the train, particularly in situations where visibility may be limited.

While there are other means of communication and signaling in the railroad environment, the horn's primary purpose is to enhance safety by providing an audible warning. It plays a vital role in ensuring that individuals near the tracks are aware of the train's approach, allowing them to take appropriate precautions. Other options, such as indicating the train's speed or communicating with other locomotives, do not align with the specific and immediate function of the locomotive horn in the context of safety protocols. Thus, option B is not only correct but fundamental to the operational safety measures in train operations.