The National Highway Traffic Safety Administration has decided that they do.

The distinct buzz or humming sound that cities produce comes primarily from motor vehicles. Tires on roads, accelerating engines, and that Doppler whoosh of boxy objects speeding by all contribute to the noise. Change the sound of cars, and you could effectively change the sound of cities.

For several years now, we have in fact been speeding toward this very opportunity. Hybrids and electric vehicles are infamously silent at low speeds, and they’ve been gaining market share at a fast enough rate to alarm pedestrian advocates – and particularly the blind – who rely on the noise of approaching vehicles for safety. Carmakers and government regulators have been investigating options for synthetic sounds that might be added to quieter cars to address this. And that prospect has had some imaginative engineers envisioning a future that sounds dramatically different – pleasanter, even – than our current world.

"The opportunities associated with that are great," acoustic engineer Nick Antonio told me last year, when Cities looked at the science of sound in cities. We've been daydreaming about it every since: Could we replace the sound of traffic with birdsong, owl hoots, waves crashing, wind chimes? If we could make cars sound like anything we want, in orchestra with each other, where would you start?

Turns out that moment is arriving now. Earlier this week the National Highway Traffic Safety Administration finally published its proposed “quiet car rule,” mandated by the Pedestrian Safety Enhancement Act of 2010, setting out standards for what the quiet cars of the future must sound like. And the long-awaited answer: They must sound like... cars.

To be specific, try one of the sample sound files the NHTSA released alongside this week's notice of proposed rulemaking:

Or maybe this?

Getting excited? Try this one:

NHTSA is projecting that the new rule, due to be finalized by early 2014, could prevent 2,800 pedestrian and cyclist injuries over the life of each model year of hybrid vehicle (the government calculates this as the equivalent of 35 lives saved). Future models won't have to literally project from speakers recordings of actual internal combustion engines (although researchers did consider this option). But with what NHTSA considers to be some degree of flexibility, carmakers will have to match the "acoustic signal content" of traditional cars driving at under 18 miles an hour. Vehicles of the same make, model and year will have to produce the same sound.

"In the holistic soundscape that we all face as human beings in the world, it would be great to be able to introduce more natural sounds into the environment," Antonio says this week, when we checked back in with him following the announcement. In an ideal world, he imagines designing whole new soundscapes. "But practically," he says, "and at the end of the day this is a very practical document intended to save a lot of lives, it has to be like this."

This moment, though, does make us wonder: Won’t it be weird – or mark a missed opportunity – if two or three decades from now we’re all driving around in naturally quiet and futuristic cars that synthetically sound like PT Cruisers circa 2000? In the graphic design world, there’s a word for this kind of dissonance: skeuomorphism. When you click on the icon of a floppy disk to save a file on your laptop, that’s a skeuomorph, a graphic element that taps into our collective memory of some utility from the past.

A similar concept exists with sound, in cell phone ringtones that blare like brassy landlines, or alarm-clock apps that wake you in the morning with the frantic beeping of an old analog clock (if anyone knows a more sound-specific word for skeuomorphism, or wants to help us invent one, please meet us in the comments section). But all of these sounds – even the floppy disk – are sort of sentimental. The sound of traffic, on the other hand, is a solution to the quiet-car problem but also a problem in and of itself.

For now, safety concerns must trump our daydreams for a more aurally enlightened city. But it would be a shame if the metropolis of the future unnecessarily sounds as cacophonous as it does today, in spite of these advances in technology, all because we couldn't retrain ours ear to associate the approach of a dangerous vehicle with something other than the internal combustion engine. This potential future – in which we enshrine a skeuomorph of traffic racket – hints at a sociological challenge as much as an engineering one.

"If people were used to the sound of birdsong 30 years ago," Antonio says, "then people wouldn’t step out [into the street] when they heard birdsong. They would look around."

So how do we get there? Antonio believes it's still possible over time to gradually transition ourselves away from the din of traditional cars to something we'd chose in that ideal world. We have no idea what kind of noise this would produce in the interim (a mashup of engines whirring over waves crashing?), but the prospect will at least give us something to ponder while we wait.

In the meantime, because you are probably also wondering about this: The proposed rule includes a prohibition against customized modifications of the synthetic sound system. So no, you cannot help the blind by having your Prius tricked out to sound like a Ferrari.

Top image: Toru Hanai/Reuters

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