The danger of the near-silent sound of an electric car was quickly identified by the U.S. National Federation of the Blind Committee when they ran tests to determine if blind pedestrians could hear a hybrid passing by. It turns out that hybrids like the Toyota Prius are so silent as to render their approach imperceptible to the vision impaired.
Pedestrian Safety Enhancement Act of 2008 was followed by the Pedestrian Safety Enhancement Act of 2009, initiated by the U.S. House of Representatives to study what minimum level of sound is necessary to protect pedestrians from the hazards of the quiet electric car. Awaiting those results, a number of carmakers have taken the initiative to develop methods to introduce some artificial sound to alert pedestrians.
Perhaps the most novel approach to increasing the sound of an electric car is the effort Nissan has expended for their Leaf EV to reproduce the sound similar to the vehicles in the cult classic movie, "Blade Runner." Other developers are using the sound of a gasoline engine, a flock of birds, and a combination of jet airliner and F1 race car. If commerce has its way, the ability to download a choice of sounds could make EV sound effects as popular as smart phone "ring tones." Until their use becomes law, installing a hybrid sound effects package could even qualify you for a discount on your electric car insurance since it could potentially save lives.