The noise of an internal combustion engine provides important feedback not only for drivers, but for pedestrians. For the vision-impaired pedestrian, the sound a car makes may be the only warning that it is approaching at all. Hence electric cars, which produce no engine noise at all, present a problem.
To solve this Jaguar is rolling out their Audible Vehicle Alert System, designed by sound engineers:
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I still think consumers should be able to download EV sounds of their choice. Then again, perhaps people would abuse the technology and select obnoxious audio (farting noises, barnyard animals, engine sounds designed by Kanye, etc.).