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Saturday, August 18, 2012

More about car horns and interfaces

This is just a short update on this week's post about car horns. I received some feedback from readers that a half second interval used as the threshold between a mere toot and a full-on honk was far too long. I must admit that I just threw that figure out there as an example and never actually intended it to be used directly.

Let's look at why. Perhaps you are moving at 75 mph. This is not too much of a stretch, since that was the speed limit for a good chunk of the drive between Colorado Springs and Denver in the late '90s. I assume it still is, but eventually urbanization of that corridor will drive it down. (Perhaps this has happened since my last visit.)

Anyway, at 75 mph, you're going 110 feet per second. In half a second, that's 55 feet. Rough metric equivalents would be 120 km/h and 33 meters per second. No matter how you slice it, that's a long way to go before your horn kicks in!

My second thought was to then use some kind of speed trigger, such that a tap at "parking lot" speeds gives one noise and anything higher does the normal thing. That was also rejected as violating the principle of least surprise with something that's intended to improve safety, not hurt it.

Ultimately, it looks like the best thing to do would be to have a second button totally separate from your usual horn trigger. All it would do is make the alternate noise. You might make the case for having it automatically switch to the louder noise above a certain speed if only because you couldn't hear it otherwise. Then again, maybe you really do just want to whisper in a hurricane.

Is the user always right?