What will help improve acoustic ecology
More and more various electric vehicles have appeared on the roads and sidewalks. Electric cars, electric bikes, electric mopeds take the place of their predecessors with internal combustion engines. Electric scooters and other micro-vehicles ride the streets.
Electric transport has a positive effect on the ecology of the city and agglomerations in the broadest sense of the word.
Locally, the emission of exhaust gases is reduced, the acoustic ecology is improved by reducing the noise of vehicles (the hum of internal combustion engines disappears). Micromobility vehicles increase the personal mobility of the population.
However, with the spread of electric transport, new difficulties also appear – the number of collisions with pedestrians is increasing. This is not only due to the fact that electric transport can pick up speed faster, but also because it is quiet and has low acoustic visibility at low speeds. Electric vehicles are even classified as a silent vehicle, which, according to the national legislation of various countries in North America, Europe and Asia, must be equipped with a special acoustic device that makes sounds when driving – the AVAS system (acoustic vehicle alerting system).
Requirements for AVAS systems are regulated by national and international regulations FMVSS 141, GB7258, EU 540/2014, UN R138.01.
These documents also define the maximum sound level (75 dBA) emitted by the AVAS system.
The visibility of an AVAS-equipped vehicle to a pedestrian will be determined not only by vehicle characteristics, travel speed, road surface types, AVAS sound types and loudness, but also by the acoustic characteristics of the environment.
Ceteris paribus, the visibility of an electric car in a noisy city yard can be sufficient, and in a park area or countryside it can be excessive. In this case, the damage to acoustic ecology in this case can be even greater than the noise of an internal combustion engine.
We conducted an experiment that assessed the visibility of vehicles (a car with an internal combustion engine, an electric car with the AVAS system on and off) on a quiet country road.
Visibility was determined using the “fixation time” – the time from the moment the expert acoustically recorded (heard) that a car was moving in his direction until the moment the car reached him. Passages of an electric vehicle with the AVAS system turned on were with two volume options – when the AVAS system was operating with a sound level of 75 dBA (maximum allowed) and a sound level of 69 dBA (twice as quiet).
The results showed that, operating at acceptable volume levels, the AVAS system in the countryside will provide excessive visibility, that is, pedestrians will hear the approach of an electric car for 25-55 seconds at a speed of 10 km/h and 25-30 seconds at a speed of 20 km/h. These visibility values are several times higher than those for a conventional ICE vehicle.
None of the regulatory documents indicates the possibility of an adaptive mode of operation of the AVAS system – such a mode in which the volume of operation is selected based on the acoustic environment around.
Such a mode of operation could reduce the noise impact on the environment and improve the acoustic environmental friendliness of the AVAS system.