Some years ago I had the good fortunate to have Ferran Mocholí Belenguer as a student in the Master’s Degree in Acoustic Engineering that we teach at Campus Gandia, and he was one of the most enthusiastic students I’ve ever had. One day, at the end of the class and on his way out to the parking lot, he asked me to supervise his Master’s Thesis (TFM). At the time, he was getting his master’s while he was working as a researcher in training at the ITACA Institute, prompting him to combine his TFM with his line of research, focused on intelligent transportation systems and acoustics. He told me how the fact that electric vehicles were silent was causing a new type of accident. Although it reduced noise pollution from traffic, it was leading to an increase in pedestrian runovers, since they could not hear the electric vehicles approaching. He also told me that there was little research on the subject and that he would like to do “something”. I remember that while we were talking it over, an electric car was approaching us, maneuvering in reverse. We didn’t realize it until it was nearly upon us. We immediately smiled at each other. Without a doubt, this corroborated the need for this line of work.
To tackle this problem, the EU had already approved a regulation (although it had not yet entered into force) whereby all electric cars had to emit a sound or artificial noise, in order to alert pedestrians of their presence. Obviously, safety is the prime concern in these cases, but there is no escaping the fact that the benefits of reducing noise pollution would be largely wasted and that absurd situations could arise with the accumulation of electric vehicles.
In this context, we wanted to answer a series of questions that would allow us to discover the difficult balance between warning sufficiently while contaminating as little as possible. Alongside his research team members, Antonio Mocholí Salcedo and Antonio Martínez Millana, he used his ingenuity to design the experiment, develop a suitable device and develop psychoacoustic perception tests. He tried sounds with different characteristics (intermittent tone, combustion engine and synthesized engine), since not all sounds are perceived equally, nor are they equally pleasing or annoying. In addition, he carried out tests in different urban environments and emitting the alert sound at different levels.
The results were quite illuminating: first of all, the alert sounds that are best perceived are precisely the most annoying ones. This is the case of the intermittent tone. This means that to alert with a more pleasant sound (synth engine) more decibels are needed. Secondly, in quiet surroundings, the level of the alert sound can be greatly reduced while maintaining the effectiveness of its task. This is especially relevant, since the level of the sound emitted could be dynamically adjusted to the minimum necessary in each scenario. Third, and perhaps the most surprising and relevant result is that we were able to verify that the levels established by the European Union (between 55dB and 76dB) are excessively high, especially in quiet environments (see figure). This means that we are emitting noise pollution needlessly, so a revision of the regulations would be advisable.
After defending his TFM, I told Ferran that he couldn’t leave it there. Undeterred, a few months later I had a draft scientific article in my inbox. The article was finally published in the April issue of IEEE Transactions on Intelligent Transportation Systems, one of the most important journals in its field. We hope that this research can one day serve to reduce noise pollution while maintaining safety levels.
In memory of Ferran Mocholí Belenguer.
The referenced article is accessible in:
Mocholí Belenguer, A. Martínez-Millana, F. S. Castells Ramón and A. Mocholí-Salcedo, “The Effectiveness of Alert Sounds for Electric Vehicles Based on Pedestrians’ Perception,” in IEEE Transactions on Intelligent Transportation Systems, vol. 23, no. 4, pp. 2956-2965, April 2022, doi: 10.1109/TITS.2020.3025499.
Full Professor, Department of Electronic Engineering of the UPV
Professor at Campus Gandia and Researcher at the ITACA Institute