There are some things technology needs help with.
The adage that children should be seen and not heard could just as easily be applied to electric vehicles. OK, sure, for the EVs it wasn't an intentional thing, it's just that with a gasoline-powered engine there's that whole pesky combustion process that makes a fair amount of noise. If you want to sneak up on pedestrians in one of these cars you need to either keep the revs super low or do it in neutral, if sneaking up on pedestrians is your thing of course.
In an electric car you can fly right up to pedestrians, or animals, or any other life form that's next to the road and scare the living daylights out of them by blasting the horn. That's the fun part of it, but there's an opposite part to that too. Stumbling drunks, lost pets and even visually impaired people can often avoid being hit by some sort of motorized vehicle because they can hear it coming, even new modern ones with the most advanced exhaust systems. As with most things that present a danger to human life, there will be loads of people campaigning to change things, and so after receiving complaints that silent cars can be dangerous, the NHTSA wants to do something about it.
The ruling that all electric vehicles must make a noise is only set to take effect by September 2019. Automakers must fit external speakers that will let you know when a car is "idling," in reverse or while accelerating up to 19 mph. The cars must make simple noises, two or four tones between 315 and 5000 hertz, separated in one-third-octave intervals. The volume must increase by three decibels for every 6 mph increase in speed. Electric cars must make the sounds between 47 and 67 decibels. So in the future all electric cars will make some sort of sound that doesn't necessarily need to ape that of a normal combustion engine. We wonder if brands will develop their own unique sounds so fans can more easily identify them?