Electric vehicle warning sounds
Electric vehicle warning sounds are sounds designed to alert pedestrians to the presence of electric drive vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery electric vehicles (BEVs) travelling at low speeds. Warning sound devices were deemed necessary by some government regulators because vehicles operating in all-electric mode produce less noise than traditional combustion engine vehicles and can make it more difficult for pedestrians and cyclists to be aware of their presence. Warning sounds may be driver triggered or automatic at low speeds; in type, they vary from clearly artificial to those that mimic engine sounds and those of tires moving over gravel.
Source: Wikipedia
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