Silent but Deadly

Listen to the fake sounds that could keep electric vehicles from hitting people

May 2, 2014
May 2, 2014

The roar of internal combustion engines is a familiar sound to anyone living in a large city, but whisper-quiet electric vehicles (EVs) pose a different problem—they provide almost no audible warning for pedestrians and cyclists. Regulators are considering rules that will require EVs to make more noise, but so far there is no consensus for what kind of sound an EV should make.

“It’s important that [sounds] are audible for people who need to hear them, but not annoying for everyone else,” says Torben Holm Pedersen, Senior Technology Specialist at SenseLab, the acoustic technology unit of Danish technology company Delta. Pedersen and the team at SenseLab have developed a range of hypothetical EV sounds—you can listen to them below—and tested them for perceptibility and irritation. There are no plans yet for these designs to be used in the wild, but they have provided important data points on effective EV sound.

SenseLab experimented with four experimental sounds: Q4noise, Jet4low, Natural hum and Low friction. These were tested for “suitability”—a measure of annoyance versus effectiveness—against sounds you might hear today, like a 2010 Mitsubishi Colt (“Mitsu 1156 rpm”) or a “Big truck”.

SenseLab provided Quartz with the audio files for these samples, and this is what they sound like:

The risk of a silent accident is greatest when EVs are traveling at low speeds. Above 18 mph or so, the sound generated by tires and wind is loud enough for passersby to recognize the danger.

Many EVs, including the Chevy Volt and Toyota Prius, can already emit warning noises, but they are not yet legally required. Regulators have thus far focused on setting a required decibel range for EVs traveling below that 18 mph threshold. But that may not be the most effective approach. “For different types of sounds at the same pressure level [an objective measure of sound strength], audibility is very different,” Pedersen told Quartz. Varying frequency or differentiating from ambient noise can make a sound more noticeable, even at lower decibel levels.

Until regulators and and car companies find a comprehensive solution, be extra-careful when jaywalking.

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