While I may not hear your personal vehicle’s horn on the open road (typically on interstates or major highways with two or more lanes in each direction, in sparse traffic, usually in rural areas) or in traffic, you would be much more likely to hear my truck’s air horn. This is the horn that children (and some older people) want me to sound when they make an overhead pulling or yanking motion with their arms. My truck’s air horn is sounded by pulling down on a cord hanging just above the left side window in the cab. It is substantially louder than the “street” horn that I can honk by tapping the center portion of my truck’s steering wheel.
The tones of these two horns are also different. The street horn emits a relatively weak, high pitched monotone that sounds like that from some personal vehicles. My truck’s air horn’s tone is lower, but still a monotone—not the deep fog horn or low muscular blare coming from some other trucks. As such, my truck’s air horn is not particularly impressive, just loud.
However, that’s not the reason I don’t show it off when pedestrians or people passing by in personal vehicles request it. Other pedestrians or motorists are almost always within earshot and it is too likely to startle, fluster, annoy and/or anger them. Truck drivers use their air horns mostly to signal or warn other truckers in truck stops, dock areas and other places where trucks are operating in close quarters. So we’re accustomed to hearing and responding to them.
In the most sudden, dangerous traffic situations I have experienced with personal vehicles, I have had to take fast action with my truck’s two most important controls–steering and brakes—to avoid collisions. I haven’t had time to reach for the air horn or honk the street horn. The personal vehicle drivers have been unaware of the hazards they were causing and would not have had time to assess and respond effectively. Rapidly proceeding our separate ways following these encounters have rendered impractical any thought of admonishing honks from me, and I am doubtful about their effectiveness anyway. So in summary, it is very unlikely that you will hear my air horn or street horn on the road.
However, other truck drivers may use their horns more actively. In rush hour traffic, I have heard a few other truck drivers honk to warn personal vehicle drivers who seemed about to, or who had, cut them off.
When you are around a truck and hear its air horn, stay out of its way, get out of its way or take other evasive action as soon as possible.