It's a requirement that many such vehicles will already meet, but the US National Highway Traffic Safety Administration has now detailed just what sort of sounds all hybrids and EVs will have to make when they're travelling at speeds under 18 miles per hour. Namely, they'll have to make a sound that's loud enough to be heard over ambient city noise, that changes to match the vehicle's speed, and that also remains audible as the vehicle is idling. The agency isn't requiring any one specific sound, however, and says that automakers will have a "significant range of choices" available to them -- they will be required to use the same set of sounds for each vehicle of the same make and model, thoug
