Link. It's H.R. 5734 - The Pedestrian Safety Enhancement Act of 2008 Silent cars sound like a great idea - until you (and possibly your dog) are riding on the hood of one. Like the article says "Cars should sound like cars."
When they say 'silent,' does that mean that dogs can't hear it too? Perhaps people should re-learn how to use their horns when they see someone doing something dangerous.