As electric vehicles become increasingly common on roads worldwide, researchers at Chalmers University of Technology in Sweden have conducted a groundbreaking study revealing that one of the most prevalent warning signal types emitted by these vehicles is particularly challenging for humans to locate. The research, published in The Journal of the Acoustical Society of America, investigated how well people can identify the source of three common Acoustic Vehicle Alerting System (AVAS) signals used in hybrid and electric vehicles traveling at low speeds.
The Experiment
The study involved 52 test subjects who were placed in Chalmers’ acoustics laboratory within soundproof, anechoic chambers. The participants were surrounded by 24 loudspeakers arranged in a ring at chest height, simulating real-world conditions such as those found in larger car parks. The test subjects were tasked with identifying the direction of various simulated vehicle sounds – including signals from one, two, or more electric and hybrid vehicles, as well as the sound of an internal combustion engine – mixed with pre-recorded background noise from a quiet city car park.
Key Findings
The results showed that all three AVAS signal types tested were more difficult for participants to locate than the sound of a traditional internal combustion engine. One particular signal, consisting of two tones, proved especially problematic when emitted by multiple vehicles simultaneously. None of the test subjects were able to successfully locate all instances of this two-tone signal within the allotted ten-second time frame. This difficulty in localization was particularly pronounced when multiple vehicles were emitting the same signal type.
Implications for Safety
Current international regulations mandate that electric and hybrid vehicles traveling below certain speeds (20 kph in Europe, China, and Japan; 30 kph in the United States) must emit warning signals to alert pedestrians, cyclists, and other non-vehicle users. However, these regulations focus primarily on detectability rather than the ability to locate the sound source or determine the number of vehicles involved. The researchers emphasize that in real-world scenarios, such as busy car parks, multiple vehicles of the same make and model may emit identical AVAS signals, potentially creating dangerous confusion.
Future Research Directions
The study’s authors, including Leon Müller and Wolfgang Kropp from Chalmers University’s Department of Architecture and Civil Engineering, stress the need for further research into how people perceive AVAS signals in various traffic situations. Their follow-up studies are already investigating how these warning signals are perceived and their potential impact on non-road users. As the number of electric vehicles on the road continues to grow, finding an optimal balance between detectability and localization of warning signals while minimizing negative impacts on the public will be crucial for enhancing overall traffic safety.
