As the era of the electric car dawns and more such cars will be on the roads, safety issues are beginning to get increasing attention. The fact that cars with only electric motors run almost silently may be good for the environment but can be a danger to pedestrians. It’s already bad enough that there are pedestrians who are walk around with earphones blocking out ambient noises that they do not realise a car is approaching them. With electric cars, even pedestrians who can hear may not know a car is coming up behind them.
For the past few years, safety authorities in some countries have begun to introduce new regulations that require electric vehicles to ‘make noise’ as a safety measure. The U.S. Department of Transportation’s National Highway Traffic Safety Administration (NHTSA), for example, added such a requirement for all new hybrid and electric light-duty vehicles sold in the USA. The new federal safety standard is intended to help pedestrians who are blind, have low vision, and other pedestrians detect the presence, direction and location of these vehicles when they are traveling at low speeds.
Under the new rule, to come into effect in September this year, all hybrid and electric light vehicles with 4 wheels and a gross vehicle weight rating of 10,000 pounds (4,545 kgs) or less will be required to make audible noise when traveling in reverse or forward at speeds up to 30 km/h. At higher speeds, the sound alert is not required because other factors, such as tyre and wind noise, provide adequate audible warning to pedestrians.
New EU directive to make noise
Since the beginning of July 2019, a new EU directive has made it mandatory to install a warning sound generator in electric cars in Europe. This stipulates that initially in newly certificated hybrid, electric and fuel cell vehicles – also trucks and buses – an Acoustic Vehicle Alerting System (AVAS) must be installed for the protection of other road users.
The warning is mandatory up to a speed of 20 km/h and the Directive formulates the parameters for how an AVAS warning may and may not sound in great detail. This applies for example to the minimum and maximum sound volume, and to certain sound components.
How manufacturers are meeting the requirement
It is subject to these and many other regulations that the sound experts of the acoustic test facility at the Mercedes-Benz Technology Centre in Germany are working on giving a ‘voice’ to the electrified Mercedes-Benz models. Special microphones in the exterior sound testing facilities are used to develop an individually configured e-sound for each electric model.
Simulations, measurements, evaluations and detailed improvements continue until the result is perfect. During the subsequent test drives, there is a particularly sensitive passenger on board – the artificial head. This registers the tiniest noises, and comes impressively close to human hearing.
The Mercedes-Benz AVAS sound differs only slightly for the EU, Japan and China. There are other requirements for the USA, for example concerning the sound volume. Furthermore, the stationary vehicle must already generate a sound when a gear is engaged, becoming louder up to 30 km/h. Switching off the AVAS by the customer is prohibited in almost all countries.
