Final answer:
You should use your horn to avoid accidents and alert others of your presence, especially on roads with limited visibility, like narrow mountain roads. Additionally, understanding the Doppler shift of emergency vehicle sirens can guide you on when to yield the right of way, which is critical to road safety.
Step-by-step explanation:
You should use your horn when it is necessary to avoid accidents. This includes situations where you need to alert others of your presence to prevent a collision. An example of this would be on narrow mountain roads where visibility is limited; drivers should drive as far to the right as possible and sound their horn when they cannot see at least 200 feet ahead. In this scenario, using the horn serves a safety purpose by notifying other drivers that may be around a blind curve that someone is approaching.
In other scenarios, such as a woman pushing a baby stroller down the street or two cars stopped at an intersection, using the horn should only be considered if there's a risk of an accident. For instance, if a child were to run into the street, a quick honk could alert the child to danger. Similarly, if the car behind is honking at the front car at an intersection, it could either indicate impatience or that the front driver is unaware of something critical like a green light.
Understanding the Doppler shift in an ambulance siren helps in determining whether the vehicle is approaching or receding, letting you know when to yield. This is an additional consideration for safety and proper horn use on the roads.