VRRRRRRRRRRThis has been brewing pretty much ever since the second generation Toyota Prius started selling well: The NHTSA is proposing that electric vehicles and hybrids make a minimum amount of noise at low speeds (under 18 miles per hour) to make sure that they can be heard by pedestrians - especially the blind - and cyclists. At higher speeds this wouldn't be necessary because the noise made by tires on the road is sufficient to be heard, and even in most gasoline cars that's what you hear most, not the engine.
"Our proposal would allow manufacturers the flexibility to design different sounds for different makes and models while still providing an opportunity for pedestrians, bicyclists and the visually impaired to detect and recognize a vehicle and make a decision about whether it is safe to cross the street," said NHTSA Administrator David Strickland.
The sounds would need to be detectable under a wide range of street noises and other ambient background sounds when the vehicle is traveling under 18 miles per hour. At 18 miles per hour and above, vehicles make sufficient noise to allow pedestrians and bicyclists to detect them without added sound. Each automaker would have a significant range of choices about the sounds it chooses for its vehicles, but the characteristics of those sounds would need to meet certain minimum requirements. In addition, each vehicle of the same make and model would need to emit the same sound or set of sounds.
Seems like a common sense approach to me. It's not like it was a huge public health issue, as right now there are millions of hybrids on the road that can operate in electric-only mode at low speeds, and they aren't that much more dangerous than gas-powered cars as far as I can tell. But if adding a little bit of noise at low speeds can make them safer for everybody, that's a low-hanging fruit that is worth picking.
NHTSA estimates that if this proposal were implemented there would be 2,800 fewer pedestrian and pedalcyclist injuries over the life of each model year of hybrid cars, trucks and vans and low speed vehicles, as compared to vehicles without sound. (source)
As long as they pick non-annoying sounds and don't allow people to use their own (like ringtones). Can you imagine how maddening this could get?