A study from Chalmers University highlights a significant safety issue with electric cars: the difficulty pedestrians face in locating warning sounds. Researchers suggest that new alerting systems are needed to ensure safety.
As electric cars become a staple on our roads, pedestrians and other vulnerable road users are increasingly exposed to their warning signals. However, new research from Chalmers University of Technology in Sweden reveals a critical problem: these signals are difficult for people to locate, particularly when multiple electric vehicles (EVs) are in motion simultaneously.
The study, published in The Journal of the Acoustical Society of America, investigated how well individuals could discern the direction of three common types of Acoustic Vehicle Alerting System (AVAS) signals emitted by hybrid and electric vehicles at low speeds.
The researchers found that all tested signal types were harder to locate than the sound of an internal combustion engine, with one signal type being particularly challenging for test subjects to pinpoint or differentiate between sounds from single or multiple vehicles.
“The requirements placed on car manufacturers relate to detection, or detectability, not about locating sound direction or the number of vehicles involved. But if you imagine, say, a supermarket carpark, it’s not inconceivable that several similar car models with the same AVAS signal will be moving at the same time and in different directions,” Leon Müller, a doctoral student in the Department of Architecture and Civil Engineering at Chalmers, said in a news release.
Current regulations require that EVs emit warning sounds at speeds below 20 kph in Europe, China and Japan, and below 30 kph in the United States. These sounds are intended to aid pedestrians and cyclists in detecting approaching vehicles.
However, Chalmers’ research suggests that detectability is not the only concern — localization is also crucial for safety.
“The way the requirements are worded allows car manufacturers to design their own signature sounds. These warning signals are often tested without the complication of background noise. But in a real traffic environment, there are usually many different types of sound,” added Wolfgang Kropp, a professor of acoustics in the Department of Architecture and Civil Engineering at Chalmers.
The experiments, involving 52 test subjects in soundproofed chambers, aimed to simulate real conditions like those in a busy carpark. Subjects were surrounded by 24 loudspeakers playing three types of simulated vehicle sounds: one with two tones, another with multiple tones, and one with noise.
The test subjects faced significant difficulty in locating the two-tone signals, especially when multiple vehicles were in play.
“Naturally, as acousticians, we welcome the fact that electric cars are significantly quieter than internal combustion engines but it’s important to find a balance,” Müller added.
While current studies focus on detectability, there is a pressing need to explore localization and its impact on traffic safety.
“From a traffic safety point of view, it would be desirable to find a signal that’s as effective as possible in terms of detection and localization but which doesn’t affect people negatively; something our previous research has shown to be true of traffic noise,” added Kropp.
In their follow-up research, Chalmers scientists are investigating how these AVAS signals are perceived and their effects on non-road users, hoping to develop more effective warning systems for the future.