Most people use their car horns to chastize other drivers, to express their low opinion of the driving skills of drivers around them and to display their desire to hurry.
The incessant horn honking has created noise pollution problems in areas with cramped streets and high car density. In July, traffic police in Mumbai launched a "No Honking Movement" led by taxi drivers who took an oath not to honk. Last year, Shanghai banned honking downtown
But the original purpose of equipping cars with horns was safety -- to warn other drivers to help avoid collisions or other hazards, not to urge slow-reacting drivers to get moving when a traffic light changes.
Evidence is inconclusive as to whether horn honking actually reduces accidents, and some have noted that there is a tendency to shift the fault for collisions to the honked-at, rather than the honker.
A Londoner argued this case in 1912: "Drivers have escaped punishment because they hooted loudly just before killing an aged and deaf colonel, or an elderly woman, deaf, and blind of one eye, or capsizing another car and injuring three or four persons … Ordinary care and precaution would have prevented each of such accidents. Hooting, however, is counted a sufficient set-off against the lack of such care and precaution."
Research into car horn honking has indicated that those who rely heavily on the horn tend to be aggressive, impatient drivers.
Jeff Muttart, a traffic-accident reconstructionist, has studied hundreds of surveillance videos of real-life car crashes and near-crashes. In 2005, he concluded that emergency horn use is not associated with decreased accident involvement. He found that drivers never steered and honked at the same time, and usually they didn't honk at all. About half of emergency honks were meant to chastise and came only after the danger was over. The other half were just preludes to a crash. Muttart explains that our inefficient horn use is linked the fact that most drivers use their horns to express their opinion of the driving skills or lack thereof of other drivers, rather than restricting it solely for emergency use.
Ill-timed honking, even when used to warn other drivers and cyclists, can backfire, startling the honked-at, causing them to freeze or lose control of their steering. This often causes the crashes that the honker meant to avoid. Many drivers use their horns, when their brakes should have been used, instead.
Many cities have banned unnecessary horn honking, such as someone laying on the horn to let his date know he's arrived, for example, and ticket offenders.
I have to admit I'm definitely an offender in using my horn to express my opinion when confronted with bad driving, usually when someone runs a red light. But I've also used the horn for its intended use and have averted a few crashes that way -- usually when someone is backing out of a parking space without looking and is about to hit me. And I'm getting more patient with drivers who don't move as soon as the light turns green.
How about you? What kind of a honker are you?
