Horn OK Please

Many Indian trucks you come across on the road would be carrying signs of this form “Blow Horn” or “Horn Please” on the rear end. These phrases are pretty ubiquitous on trucks throughout the nation and are meant to encourage a motorist approaching from behind to explicitly sound a horn if they wish to pass.

Coming from a place where horns are very scarcely used on the roads or their usage in general is frowned upon, you might be surprised. While the origin of this phrase on the trucks may have a historical need due to single lane roads in the past, but today horns happen to be an indispensable tool while driving on many Indian roads. Kerala is one place that I know of which is quite different in this regard.

I was instructed by my driving tutor to sound a horn whenever I approached a bend, a crossing or if I was attempting to pass someone. 

Why would this be?

Firstly, the usage of side mirrors isn’t common. While this may not be true for all Indian roads and cars, yet in many cases people would simply fold their side mirrors to prevent it from breaking off while driving close in highways (worth to note here that people do not always stick to lanes or maintain distances). So its necessary to alert others to not try to swerve while you are overtaking their vehicle.

Secondly, the traffic rules and laws and their enforcement is not too strict. Motorbikes, rickshaws, bicycles, pedestrians, trucks etc. are all on the same road, and in such a scenario when you have different types of traffic coming in from different directions, resorting to horns is the best way to catch someone’s attention. You could not really be in the visual line of sight for a 360 degree view for everyone. This necessitates adopting to auditory means.

Just a bunch of interesting anecdotes. Copied from my answer on Quora on the topic https://www.quora.com/Why-do-people-blow-horns-so-much-in-India/answer/Mohita-Menon