If everybody follow simple traffic rules there's absolutely no need for the vehicle behind a truck to have the need to make the truck aware they are there.
1. Vehicle behind must keep distance, no tailgating.
2. Vehicle ahead should not change lanes before
a) Making sure the marking on the road says it is permitted.
b) Signaling the maneuver with directional lights.
c) Checking the side mirror before actually starting the maneuver.
That's basically how it works in the rest of the world. Trucks have large blind spots everywhere else, but by signalling their maneuvers in advance and with the other drivers following some simple rules, lots of places in the world (including a lot of poor countries in Latin America) get by with reserving the use of honks only for true urgent situations.
I agree and people are exeggerating the usage of horns more than it actually is.
> there's absolutely no need
But one use of horn that I found useful in India was to overtake on 2-lane hilly road. Now theoretically you should be able to see, may be hundred metres, ahead of you before you start the overtake or if you are not too keen to reach your destination, not overtake at all till you reach straight road with longer view. In practice though, trucks are slow moving and roads sometimes don't provide clear view of the road with twists and turns so it helps if you let the truck ahead of you know of your presence. Then truck dirver signals you with his hand when it is safe to overtake with his longer FOV. Apart from that, truck driver knowing of your presence can help him slow down his vehicle in case oncoming vehicle is cutting it too close for you to overtake the truck.
Is there a better way of doing this? Probably, by just avoiding any risky overtake by road markings etc. but as I said above, that could mean following the truck for few hours in the worst case. And does that mean you honk everytime you are behind a truck? Not at all.
Yes, you don't overtake if you don't have visibility because of a hill or a bend. That is enforced by traffic regulation and road markings in Europe and most of the places I've driven. And yes, that means that sometimes you get stuck behind trucks for a long time but it also means that nobody gets killed.
If you read my comment carefully, I understand that and I know how it happens around the world. But I personally would prefer to sometimes hear a horn rather than having to drive behind a slowest moving truck for hours because the hilly road has road marking catering for the worst case.
What I say above makes it sound like I think that it's sole responsibility of the drivers to keep to the rules but I do understand that the rules are much easier to follow when the vehicles are in good condition and the roads have amenities like escape routes for trucks and occasional third lanes to allow overtake, both of which require wealth and strong institutions that are not present everywhere in the world.
Still, from my experience in India (mostly in and around Delhi) what you get is not an occasional honk, it is a permanent infernal cacophony that pierces through your skull day and night.
Modern trucks in the western world have plenty of power to be surprisingly nimble negotiating ascents, it is downhill that things get more complicated for modern trucks.
1. Vehicle behind must keep distance, no tailgating.
2. Vehicle ahead should not change lanes before
That's basically how it works in the rest of the world. Trucks have large blind spots everywhere else, but by signalling their maneuvers in advance and with the other drivers following some simple rules, lots of places in the world (including a lot of poor countries in Latin America) get by with reserving the use of honks only for true urgent situations.edit: line-breaks