Challenges in Locating Electric Vehicle Warning Signals
A recent study by researchers at Chalmers University of Technology has uncovered significant challenges in how people perceive warning signals from hybrid and electric vehicles moving at low speeds. The research, conducted in a controlled acoustics laboratory, tested 52 participants’ ability to locate three common types of Acoustic Vehicle Alerting System (AVAS) signals.
The study’s findings were striking: all AVAS signals were harder for participants to locate compared to the sound of an internal combustion engine. One particular signal, consisting of two tones, proved especially problematic. When this signal was simulated to come from three vehicles simultaneously, none of the test subjects were able to correctly identify all instances within a ten-second time limit. The majority struggled to distinguish the direction of the sound or determine whether they were hearing one, two, or more vehicles.
“The requirements placed on car manufacturers relate to detection, not about locating sound direction or the number of vehicles involved,” notes Leon Müller, a doctoral student at Chalmers’ Department of Architecture and Civil Engineering. “But imagine a supermarket car park where several similar car models with the same AVAS signal are moving simultaneously in different directions. It’s not inconceivable that this could lead to confusion.”
Current international standards require hybrid and electric vehicles to emit warning signals when traveling below certain speeds – 20 kph in Europe, China, and Japan, and up to 30 kph in the United States. These regulations focus on detectability rather than localization or distinguishing between multiple sources.
The experiments were conducted in Chalmers’ soundproof, anechoic chambers where participants were surrounded by 24 loudspeakers. The setup aimed to simulate real-world conditions, such as those found in larger car parks, by playing various AVAS signals mixed with background noise recorded from a quiet city car park.
The results showed that participants could easily locate the sound of an internal combustion engine, which consists of short pulses across all frequencies. This is in contrast to the fixed tones used in many AVAS signals, which are harder for the human ear to perceive. The familiarity of the internal combustion engine sound may also contribute to its easier localization.
“Naturally, as acousticians, we welcome the fact that electric cars are significantly quieter than internal combustion engines, but it’s crucial to find a balance,” Müller explains. The researchers highlight a need for further investigation into how people react in real traffic situations involving multiple electric vehicles emitting the same AVAS signals.
The study, titled ‘Auditory Localization of Multiple Stationary Electric Vehicles,’ is published in The Journal of the Acoustical Society of America. The researchers are now conducting follow-up studies to investigate how AVAS signals are perceived and their potential impact on non-road users.
From a traffic safety perspective, Wolfgang Kropp, professor of acoustics at Chalmers, emphasizes the importance of finding an AVAS signal that is both effective for detection and localization without negatively affecting people. “Our previous research has shown that traffic noise can have significant impacts. We need to balance safety with other factors.”
