Electric vehicles and their warning sounds are hard to detect when moving at low speeds

With the increasing prevalence of electric cars, vulnerable road users are being exposed to a growing number of warning signals. However, new research from Chalmers University of Technology in Sweden reveals that one of the most commonly used signal types is particularly challenging for people to pinpoint—especially when several similar vehicles are moving at the same time.

In a recent study, researchers at Chalmers University examined how effectively people can identify the direction of three commonly used warning signals—known as AVAS (Acoustic Vehicle Alerting Systems)—emitted by electric and hybrid vehicles at low speeds. Their findings revealed that all three signals were more difficult to locate than the sound produced by traditional internal combustion engines. In one case, most participants struggled to identify the direction of the sound or to tell whether it was coming from one vehicle or multiple vehicles at once.

“The current regulations for car manufacturers focus on whether the signal can be detected—not on whether its direction can be identified or how many vehicles are emitting it,” explained Leon Müller, a PhD student in the Department of Architecture and Civil Engineering at Chalmers. “But consider a supermarket parking lot—it's entirely possible that several similar electric cars, using the same AVAS sound, could be moving in different directions at the same time.”

Electric and hybrid vehicles today comply with international acoustic warning standards. In regions such as Europe, China, and Japan, cars must emit a sound below 20 km/h to alert pedestrians, cyclists, and other non-drivers. In the U.S., the requirement applies to vehicles traveling under 30 km/h.

“Manufacturers are allowed to create their own distinctive alert sounds based on how the regulations are written,” said Professor Wolfgang Kropp, an expert in acoustics at Chalmers. “These sounds are often tested in controlled environments without background noise. However, real traffic settings are full of diverse ambient sounds, which can affect how well these warning signals are perceived.”

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Trying multiple different signals

The study involved around 52 participants and was carried out in Chalmers University’s acoustics lab, using soundproof, echo-free (anechoic) chambers. The goal was to replicate real-world conditions, such as those in large parking lots. Participants were placed at the center of the room, surrounded by 24 chest-height loudspeakers arranged in a circle.

These speakers played three types of simulated warning sounds from electric and hybrid vehicles—representing one, two, or more vehicles—as well as a sound from a traditional combustion engine. The warning signals included a two-tone sound, a multi-tone signal, and a noise-based alert.

Each sound was played from a distance of about 7.5 meters and combined with background noise recorded from a quiet urban parking lot. Upon hearing a signal, participants were asked to quickly identify its direction. The two-tone signal, especially when emitted by three vehicles at once, proved to be the most difficult to pinpoint—none of the participants could accurately locate all of the two-tone signals within the 10-second time frame.

New signal types needed

The participants in the study had little trouble identifying the direction of sounds from internal combustion engines. According to Leon Müller, this is because those engines produce short bursts that span a wide range of frequencies, making them easier for the human ear to detect compared to steady tones at a single frequency. Additionally, people may recognize these engine sounds more easily due to their familiarity.

“As acousticians, we certainly appreciate how much quieter electric cars are compared to traditional ones,” Müller notes, “but it’s crucial to strike the right balance.”

Up until now, most studies have concentrated on how easily electric vehicle warning sounds can be detected, often measured by “detection distance.” However, no earlier research has explored how people respond when multiple vehicles emit the same warning signal simultaneously. The Chalmers researchers highlight a significant gap in understanding how pedestrians and other non-drivers perceive electric vehicles in such scenarios.

“From a traffic safety standpoint, the ideal warning signal would be one that is easy to detect and locate,yet doesn’t cause discomfort or irritation—something we’ve found to be a common issue with general traffic noise,” explains Professor Kropp.

In their ongoing work, the team is now examining how people experience AVAS signals more broadly, including their psychological and behavioral effects on pedestrians and other vulnerable road users.