What is the primary function of a locomotive’s horn?

The primary function of a locomotive’s horn is to signal other trains and approaching vehicles. This is a crucial safety feature in rail operations, serving to warn those nearby that a train is in the vicinity. The horn is used in various situations, such as when the train is approaching a grade crossing, in low visibility conditions, or when another train is in close proximity on parallel tracks. This audible warning helps prevent accidents by giving people and vehicles enough time to react and move out of the way.

Using the horn effectively contributes to the overall safety of rail transport, maintaining clear communications and ensuring that both track workers and the general public are aware of the train's movements. The other options do not align with the primary intent of the horn in terms of train operation; the horn is not designed for mechanical alerts, speed indication, or passenger information.