When is it appropriate to use a vehicle's horn?

The appropriate use of a vehicle's horn primarily revolves around safety and alerting others in emergency situations. Using the horn to signify an emergency helps convey an immediate need for attention from other road users. For instance, if a driver needs to warn another vehicle of an impending collision or to alert pedestrians of an oncoming vehicle in a situation where they may not see it, the horn serves as a critical communication tool.

The other options touch upon less appropriate uses of the horn. Expressing frustration or greeting someone with the horn does not serve to enhance safety and can actually contribute to road rage or distractions. Similarly, using the horn whenever one feels like it disregards the need for appropriate and responsible driving, potentially causing confusion or annoyance for other drivers on the road. Thus, the best practice is to reserve the horn for situations that directly relate to safety and alertness.