An acoustic vehicle alerting system, or AVAS, is a speaker-based system installed on electric and hybrid vehicles that produces artificial sound to warn pedestrians the vehicle is nearby. Because electric motors are nearly silent at low speeds, these vehicles pose a real collision risk to anyone who relies on hearing to detect approaching traffic. AVAS solves this by playing a continuous sound through loudspeakers mounted beneath the vehicle’s body, coordinated with real-time data on speed, direction, and distance.
Why Electric Vehicles Need Artificial Sound
Traditional cars announce themselves. Engine combustion, exhaust rumble, and mechanical vibration create a constant audio signature that pedestrians process without even thinking about it. Electric vehicles strip nearly all of that away. At highway speeds, tire noise and wind resistance fill the gap. But below about 20 to 30 km/h, an EV can be virtually inaudible, which is exactly the speed range where vehicles interact most closely with pedestrians, cyclists, and children at crosswalks, parking lots, and residential streets.
The risk is especially serious for blind and visually impaired pedestrians. The World Blind Union has emphasized that AVAS must be loud enough for someone to detect the presence and direction of an approaching vehicle at a distance that allows a safe crossing decision. The organization has also pushed back against regulations that allow vehicles to remain silent while stationary, arguing that a quiet vehicle sitting at an intersection with its motor running still needs to be audible. Japan’s regulators agreed, recommending that the pause function (which would let drivers mute the system) be prohibited entirely.
How AVAS Works
The hardware is straightforward: one or more loudspeakers installed under the vehicle’s exterior panels, connected to a control unit that pulls data from the car’s speed sensors, gear position, and other systems. The sound changes dynamically as the vehicle accelerates, decelerates, or reverses. This isn’t a simple beep or static tone. The system continuously adjusts pitch, with regulations requiring a pitch shift of at least 0.8% per km/h between roughly 5 and 20 km/h, so pedestrians can intuitively sense whether the vehicle is speeding up, slowing down, or holding steady.
The sound must fall within specific frequency bands. Under the international UN Regulation No. 138, two frequency bands between 160 Hz and 5,000 Hz must meet minimum sound pressure levels. The U.S. standard uses a slightly narrower range, requiring two or four frequency bands between 315 Hz and 5,000 Hz. These ranges were chosen because they cover frequencies the human ear detects well, even in noisy urban environments.
When AVAS Activates and Shuts Off
AVAS is not meant to run at all times. Once a vehicle reaches a certain speed, tire and wind noise become loud enough on their own. The threshold where AVAS is allowed to stop, called the “crossover speed,” differs between the U.S. and Europe. In the U.S., the system must emit sound during forward motion up to 30 km/h (about 19 mph) and whenever the vehicle is in reverse. The EU sets a lower crossover speed of 20 km/h (about 12 mph), based on evidence that most EVs produce sufficient natural noise above that point.
In the U.S., the system must also produce sound any time the vehicle’s propulsion system is activated, including when stationary, unless the gear selector is in park or the parking brake is engaged. This means an EV idling at a red light with the transmission in drive will still emit a low-level alert sound.
U.S. and EU Regulations
The U.S. regulates AVAS through Federal Motor Vehicle Safety Standard No. 141, which applies to electric and hybrid passenger cars, SUVs, light trucks, buses, and low-speed vehicles with a gross weight of 10,000 pounds or less. The standard was published in December 2016, with a phased rollout: 50% of new vehicles had to comply by September 1, 2019, and full compliance for all covered vehicles took effect September 1, 2020.
In Europe, UN Regulation No. 138 made AVAS mandatory for all newly registered electric vehicles starting July 1, 2019, for new vehicle types and July 1, 2021, for all new registrations. The two regulatory frameworks share the same goal but differ in details. The U.S. requires sound during standstill (when in gear) and uses the higher 30 km/h crossover speed. Europe uses the lower 20 km/h threshold. The U.S. minimum sound levels at testing speeds also differ slightly from the European values, meaning automakers selling globally need to calibrate their systems for each market.
One early concern from the World Blind Union was that proposed minimum sound levels were too quiet. Research conducted at Louisiana Tech University found no statistical difference in test subjects’ ability to hear a quiet vehicle with or without AVAS at the initially proposed levels, prompting calls to raise the minimums. Regulations have since been adjusted, but the tension between making EVs audible enough for safety and avoiding unnecessary noise pollution in cities remains a live debate.
How Automakers Design Their Sounds
Regulations set the floor for volume and frequency, but manufacturers have significant creative freedom in what their vehicles actually sound like. This has turned AVAS into a branding opportunity, and the approaches vary wildly.
Porsche kept close to tradition with the Taycan, filtering recordings of actual vehicle components to recreate the rattles and whistles of classic Porsche engines in a distinctly electric package. BMW’s “IconicSounds Electric” program blends human voices with classical instruments and offers drivers five selectable modes, including “Sport” and “Expressive.” Mercedes-Benz went in the opposite direction, designing sounds for its EQ lineup that resemble natural ambience like rustling leaves or a flowing stream, intended to blend into the environment rather than stand out.
Audi’s e-tron GT takes an algorithmic approach. The base note comes from the sound of a fan in front of a cylindrical object, and the system constantly mixes 32 individual tones through an algorithm, so the sound is never exactly the same twice. Volkswagen hired composer Leslie Mandoki to create its “ID. Sound,” described as “confident and friendly, futuristic, and with a unique character.” Rivian recorded thunderstorms, animal calls, and waterfalls to build a nature-inspired audio palette. And Ford’s Mustang Mach-E features a propulsion sound designed with rapper T-Pain, drawing inspiration from Formula E, movie soundtracks, and roller coasters rather than traditional engines.
The industry is broadly split into two camps. Some manufacturers, including Audi, Ford, and Jaguar, lean toward sounds that echo combustion engines with a futuristic edge, keeping the experience familiar. Others, including Nissan and General Motors, aim for something entirely new: organic, musical, or immersive sounds that redefine what a car sounds like from the outside.
Noise Pollution Concerns
AVAS solves one problem while potentially creating another. Adding artificial sound to millions of vehicles reintroduces noise into urban environments that were on track to get quieter as electrification grows. Regulations cap maximum sound levels to address this, and the relatively low crossover speeds (20 to 30 km/h) mean the system is only active in exactly the situations where pedestrian interaction is most likely. Still, the cumulative effect of many AVAS-equipped vehicles in a dense city remains an open question for urban planners and acoustics researchers.
Some engineers are exploring directional speaker technology that would project sound only toward detected pedestrians rather than in all directions. Early prototypes pair cameras or sensors with targeted speakers, reducing the overall noise footprint while still alerting the person who needs to hear it. These systems remain experimental, but they represent a potential path toward balancing pedestrian safety with the quieter urban environments that electric vehicles originally promised.