Are hybrids too quiet?

Now that there are at least one million Priuses on the road, along with many other gas-electric hybrid vehicles, people are becoming concerned that the eco-friendly cars are not so friendly to the blind.

When traveling below 25 miles per hour, a Prius runs silently on electric power. While some may welcome the reduction in traffic noise, the cars make it difficult for pedestrians – particularly those who can't see – to know when they're approaching.

In April, Representatives Ed Towns (D-NY) and Cliff Stearns (R-FL) introduced the Pedestrian Safety Enhancement Act of 2008, which would require the Department of Transportation to establish minimum sound levels for all hybrid and electric vehicles.

This bill is heartily endorsed by The National Federation for the Blind:

"The National Federation of the Blind appreciates the wise and decisive action taken today by Congressmen Towns and Stearns to preserve the right to safe and independent travel for the blind," said Dr. Marc Maurer, President of the National Federation of the Blind. "The blind, like all pedestrians, must be able to travel to work, to school, to church, and to other places in our communities without being injured or killed. This bill will benefit all pedestrians for generations to come as new vehicle technologies become more prevalent. The blind of America will do everything in our power to ensure its swift passage."

Some Prius owners aren't thrilled at the prospect of having their cars' volume increased. In some online forums, the bill has been labeled the "Bell the Hybrid Act."

But if the bill passes, it will raise some questions:How would the cars make the noise? And what noise would they make?

Two grad students at Stanford have come up with an answer.

Everett Meyer, a med student, and Bryan Bai, an engineering student, came up with a system that emits sounds from palm-sized speakers placed under the front wheel wells and the back bumper. According to a press release from Stanford, their PANDA system (that's Pedestrian Awareness Noise-emitting Device and Application) is about 5 decibels quieter than a regular combustion engine from the front and 10 to 20 decibels quieter from the back. The noise is not audible from inside the car, unless you roll down the windows.

The press release described the sound as unlike a car engine, but rather "a bit closer to a muted jet engine, with some static and white noise thrown in."

Meyer and Bai have started a company called Enhanced Vehicle Acoustics.

It all sounds like a great idea, but somebody should have told them that a similar, cheaper device has already been invented.