Scientists are sounding the alarm about potential hazards associated with tones, whirs, beeps, or other sonic-alert systems by which electric and hybrid-electric vehicles generate artificial noises to announce their presence.
These warning signals — technically referred to as acoustic vehicle alerting systems (AVAS) — are being instituted in Europe and the US, and are designed to alert pedestrians, especially those who are blind or vision-impaired, to the ultra-quiet vehicles.
They operate whenever the vehicle is moving below a certain speed, generally between 20 and 30 kilometers per hour. At higher speeds, even the quietest vehicles generate enough tyre noise for warning signals not to be needed.
It sounds like a good idea, but there’s a downside.
“A lot of people are not very happy about these sounds,” says Klaus Genuit, a psycho-acoustic expert and founder of HEAD acoustics GmbH, a German company that provides sound and vibration analysis to a number of clients, including the automobile industry.
Overall, he reported at a recent meeting of the Acoustical Society of America, in Louisville, Kentucky, “more than 50% of people complain of traffic noise. Electric cars could be a good tool to reduce traffic noise, but if we add traffic warning signals, it could become worse.”
One of the biggest problems, he says, is that in designing these signals, researchers are working under the implicit assumption that only one car will be emitting them at any given time.
But in an urban setting, with a lot of slow-moving vehicles, that simply isn’t realistic. Instead, Genuit says, there could be many cars creating a cacophony of different sounds that might clash unpleasantly.
“If you mix tones, you get disharmony,” he says, referring to musical instruments to illustrate his point.
“If you have one violin, it may be good. But if you have two violins they must be tuned together.”
Also, he says, warning sounds must be designed with an eye, or ear, to their purpose, which isn’t simply to make noise, but to give warning, where warning is needed.
That means the signal must be designed so people can easily localise its source in the presence of other noises, even in complex, realistic scenarios. It also must not be disturbing to the driver, who is going to have to listen to it all the time.
Rene Weinandy, head of the Noise Abatement in Transportation Division of the German Environment Agency, carries the question a step further, wondering if these types of warning signals are even necessary.
“Is it really a wise decision to increase the noticeability of electric vehicles in traffic by making them spray poison?” he asks.
Modern internal combustion engines are also quite quiet. “Do these need AVAS, too?” he asks.
Perhaps, Weinandy says, there are less noisy ways to protect pedestrians, ranging from making the signal less aggressive, like a bicycle bell, to bypassing the warning entirely, and relying on automated pedestrian-detection and braking systems.
It’s even possible, he notes, that cars could generate signals that could be sent to handicapped pedestrians in the danger zone — signals that could be detected by their smart phones or other specially-designed devices, delivering the alert to them more directly.
Genuit adds that this process could work both ways, with handicapped people not only being warned that a car is coming, but the car being informed of a handicapped person in its vicinity. The result would be warning signals that are only emitted when the situation requires them.
That’s important Genuit says, because such signals work best if they are infrequent and only used when needed. Cacophony is not helpful.
“An overload of warning signals reduces their effectiveness,” he says.