On Horns, Turn Signals, and Connected Vehicles

The End of Traffic and the Future of Access: A Roadmap to the New Transport Landscape. By David M. Levinson and Kevin J. Krizek.
The End of Traffic and the Future of Access: A Roadmap to the New Transport Landscape. By David M. Levinson and Kevin J. Krizek.

We have long had inter-vehicle connectivity. The means are slow and loud: the horn and the turn signal, as well as eye contact between nearby drivers. But they are widely used despite their minimal effectiveness.

Horns have a variety of purposes. In the US, the horn is most commonly used to express the following sentiments:

  • “Move you idiot“, for instance, when the light changed colour.
  • “You are cutting me off,” we might get in a collision, and my pressing the horn, while pressed far too late to avert said collision, releases some frustration.
  • “You bastard, you are in my right-of-way and I am too lazy to tap the brakes, but not too lazy to hit the horn” (Alternatively “I’m an asshole, and I want the world to know it”)

In developing countries, horns have other uses.

Traffic in Enshi
Traffic in Enshi
  • I’m changing lanes … not merely, “I am requesting permission to change lanes,” but the more active, “I’m changing lanes and you have been forewarned.”
  • “I’m coming around the sharp corner with little visibility, but sufficient audibility, at too high a speed to safely brake, and don’t care to reduce my speed to a safe speed, you have been forewarned.”

Turn Signals also have their uses. In developed countries, the turn signal indicates

  • “I’m would like to change lanes, if a gap opens up, I might take it.”

In developing countries, I have observed the turn signal, particularly at steep uphill grades indicating, as near as I can tell:

  • “You should change lanes. Really, I won’t be offended, I have a heavy load I am carrying up this hill and my vehicle cannot maintain speed, and there don’t seem to be any. oncoming cars right now, though I am not liable should there be one”


This dual usage of turn signals is analogous to the awful Minnesota expression “Can you borrow me some money” which is normatively incorrect ( with a clear enough meaning) and just grates on the ears. I borrow, you lend. I lend, you borrow.

It is sometimes argued that Connected Vehicles, with a real-time broadcast of a here-I-am message could replace the horn (HEAR! I AM!) and turn signal (see me! I am!, vocalised in a quiet Horton Hear’s a Who voice no louder than a clicking turn signal contact)., But this assumes CVs were universal, and pedestrians and bicyclists were connected too (or have simply been eliminated, Wall-E style). Short of that, the horn particularly, which is almost sure-fire in annoying walkers and bikers, remains relevant as a way of forewarning.

Now of course, an automated vehicle wouldn’t be (shouldn’t be) going around sharp corners at too high a speed, so AVs could eliminate excess noise through better behaviour. Horns in retrospect would also be eliminated. AVs could possibly infer the dual meaning of turn signals from context and vehicle behaviour. After visiting China, it is clear AVs would not work in the Wild West of Wuhan, but are much more feasible in modern Shanghai, where pedestrians and bicyclists are much more likely to be rule abiding. Certainly over time, as developing areas are civilised into the ways of modern motordom, this issue will diminish. But it needs to be kept in mind that the context shapes the effectiveness.

While urban noise levels will likely decrease with advances in technology, this is due to the automation, not connectivity.

I have long felt the solution to much noise in urban environments is to blast the horn inside the vehicle. That way, whenever someone slammed the horn, they would internalise much of the noise externality they create, leading to less noise production in the first place.