Raul Sotillo is in India sharing his photos. Sound horn in back of trucks caught his attention. Here is one explanation.

One Plausible Reason Why Indians Love Honking Horns. Forbes

“No matter what they’re driving, a motorbike, a three-wheel auto-rickshaw, or a 40 year old Tata Motors truck, the horn is as important as the gas pedal. It may be more important than the brakes.  And I think I know why Indians use the car horn so much; it’s the complete disregard for side mirrors.  No one uses them. Some trucks don’t even have them. Others have their mirrors pushed closer to the vehicle because to extend them outward could invite a collision with another driver.  Cars are so close to one another on the road that mirrors simply take up too much space.  So with that in mind, truckers behind the wheel of India’s ancient truck fleet — at least 40 years old according to Singh — invite drivers to honk as a means to advise them that they are about to pass.”

Read article: https://www.forbes.com/sites/kenrapoza/2014/05/13/one-plausible-reason-why-indians-love-honking-horns/