Why California’s Musical Road Sounds Terrible


If you drive down a certain stretch of highway
in the California desert, you will hear music. It’s supposed to sound a little bit like this: [William Tell Overture, by Rossini] but instead, it sounds like this. [William Tell Overture, by Rossini,
but badly out of tune] That was the musical road
of Lancaster, California. And as you may have heard,
it’s a little bit out of tune. A lot of money was spent on that road. It was a publicity stunt for a car company
who wanted to show off how clever they are. And doing the calculations for
something like that isn’t really difficult. A musical note is a vibration in the air at
a particular frequency. And those vibrations can be made by
a violin string or synthesised by a computer or – in this case – made by vehicle tyres
hitting grooves in the road. The closer the grooves are,
the faster the vibrations, and the higher the note. So take the speed limit, divide by the frequency of the note you want, and that’s how often there should be a groove
in the road. And if people travel at the wrong speed, well,
it shouldn’t really matter. It’ll just be like slowing down or speeding up
any other piece of music: it’ll be in the wrong key, but it’ll still
sound right to most people’s ears. It won’t sound like that mess. So what went wrong? At this point, I am indebted to David Simmons-Duffin, an assistant professor of physics at Caltech, whose interests include Quantum Field Theories
and playing baroque violin. Because he was, as far as I can tell, the very first person to figure out
what went wrong: and the problem was probably the English language. Whoever did the calculations said that the
grooves should be so far apart. Let’s say, four inches for the first note. And they meant there should be
a groove every four inches. But whoever gave the instructions
to the work crew said that the grooves should be
“four inches apart”. And that was interpreted as four inches between
the end of one groove and the start of the next one. They didn’t include
the width of the groove itself. But your ears definitely do include it. The highest note on that section of
the William Tell Overture should be one octave higher than the lowest. That means the frequency should be doubled, and that the grooves should be
half the distance apart. And they are: if you don’t include
the width of the groove itself. That error means that every note is distorted
not by a fraction of its value, like if you’re travelling at the wrong speed, but by a constant amount: by the width of
the grooves. The higher the note, the greater the effect
of that distortion. And the result is the mess that you are about
to hear for a second time. And the really strange part? This is the second musical road
built in Lancaster, California. The first one, built by the car company, was
too close to residents, who complained about the constant noise. And probably this note here. So the city paved over it and rebuilt it… to the exact, same, wrong blueprints. That’s a take. That is a take. Right there. And in order to celebrate that take, I am
going to put my foot down. This is an SUV. It doesn’t, er… it doesn’t do that.

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