Electric Cars - Safety Risk? Potential Solutions?

I heard a clip on NPR this week about how electric cars could be a safety risk for blind people. They did a study on cars powered by a conventional engine vs. electric cars and, surprise, electric cars were much harder for blind people to identify as they are much quieter. I tried to google the news clip, but have been unable to find it. My knee jerk reaction was to think that the article was a little too right-leaning for NPR. I also thought that the safety risk to blind people was outweighed by the advantages for electric cars. I did a bit more poking around, and found this article that was published back in 2007 that discusses some of the artificial sounds that could be added to electric cars to make them identifiable to the visually impaired:

http://www.groovygreen.com/groove/?p=1962

Although personally I think that the quietness of electric cars is attractive, I could see some sort of sound being added to those cars for safety reasons. It seems like an action like that could help kids playing in the street, etc. As the article discusses, if a sound is to be added to electric cars, what should the sound be? This makes me think of when I was a kid, my dad added deer whistles on our van for times that we went camping and were around wildlife at nighttime. Perhaps we shouldn’t go down that route…any suggestions?