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.edit: line-breaks