The approval of the Pedestrian Safety Enhancement Act last year essentially mandated that electric vehicles or hybrids running only on electric power--devoid of the actual engine noise that makes pedestrians (particularly the visually impaired) aware that a vehicle is approaching--must now generate some sort of artificial proximity notification noise. However, although the Act mandated that EVs must make a sound, it didn't specify exactly what sound they should make. This means that every EV and hybrid manufacturer is free to make its cars sound like anything.
Toyota has released a video that explains the vehicle proximity notification sound designed for its Prius line of vehicles and demonstrates the sound with the upcoming 2012 Prius V. In the video, it is explained that Toyota's notification sound activates only at speeds below about 15 mph, uses a combination of high- and low-pitched tones to make it easily audible over city sounds, and rises and falls in pitch with the vehicle speed to give pedestrians a sense of whether the approaching Prius is accelerating or decelerating. The tone is generated by externally mounted speakers, so the driver potentially won't even be able to hear it with the windows secured.
Personally, I think the sound is a bit odd, but think I would definitely take notice if I heard it approaching. What do you think, readers? Do you like the sound or hate it? Will it improve pedestrian safety or is it just more superfluous noise pollution in an already noisy world? Sound off in the comments.