All new electrified vehicles must emit a noise at low speeds to warn pedestrians of their presence under new EU law.
The ruling applies at all four-wheeled fully electric and hybrid vehicles that go on sale from July 1.
Under the EU Regulation on the Sound Level of Motor Vehicles and EU Requirement ECE R138, electrified vehicles must have an Acoustic Vehicle Alert System (ACAS) that activates at speeds below 20kph (12mph) and be at a minimum noise level of 56dB.
According to noise control experts IAC Acoustics, 60dB would be the equivalent of conversation in an office or standing 100ft from an air conditioning unit, and about half as loud as a vacuum cleaner.
The regulation states that the ACAS should emit a noise that is “a continuous one providing the vehicle driving behaviour to other road users and pedestrians”. This means that the sound level should increase and decrease in relation to the vehicles speed to convey whether it’s accelerating, decelerating, or travelling at a consistent speed.
Some car manufacturers already have ACAS fitted to their vehicles, such as Jaguar with its I-Pace, which emits a science-fiction UFO-like warble below 12mph to warn pedestrians of its approach.
In March, audio company Harman revealed its experiments with ACAS, demonstrating a Tesla Model S that could emit the sound of a V8 petrol engine.