They silently sneak up on unsuspecting pedestrians, bicyclists, children and the blind. Unlike cars with running internal combustion engines, hybrid cars in electric-motor mode are relatively silent and give no audible clues they are approaching. The results could be deadly.

As Deborah Kent Stein of the National Federation of the Blind said in 2008, "For us, these cars are invisible."

A study authorized by the National Highway Traffic Safety found a 50 percent higher rate of accidents involving pedestrians for hybrids than other automobiles vehicles, the Wall Street Journal reported.

A report on summarized the danger this way: "A previous study found that hybrid electric vehicles are more than twice as likely to be involved in a pedestrian accident than conventional cars, when the vehicles are backing out, slowing or stopping, starting up in traffic, or going into or out of a parking space or driveway."

Toyota released a video touting what they call the "Vehicle Proximity Notification System (VPNS)" which makes the Prius sound like Luke Skywalker's landspeeder in Star Wars. A video of Nissan's LEAF demonstrates noise that sounds more like a Star Trek starship about to go into warp speed. So people don't have the flying cars promised in the 1950s, but at least they sound like flying cars.

Historically speaking, the debate is similar to the controversy when automobiles were first introduced. Cars were a lot noisier around the turn of the 19th century, but pedestrians were mentally cued to watch out for horse noises and horse speeds and would get hit by the new contraptions. In some communities ordinances were passed requiring a person with a flag to walk in front of all automobiles for safety. Those laws are no longer in place, presumably because people became used to the new sounds and dangers.

Mark Larsen at Utah State University examined fatality records MSNMoney reported. He assumed that pedestrian deaths would go up since 2000 when hybrids first went on sale. If more were on the road, then more deaths should result if there was a danger. "The data showed pedestrian deaths fell over the observed time frame," MSNMoney reported.

But if the problem is people getting audio clues that a car is nearby, those science fiction warp engine noises may not get the job done.

After years of various calls for standards, last week the National Highway Traffic Safety Administration and the Volpe National Transportation Center recommended what sounds hybrid and electric cars should make.

"Researchers concluded the best solution was to ensure that electric and hybrid vehicles emit the same sound as vehicles with an internal combustion engine," reported. "Researchers suggested actual recordings of conventional cars, or a digitally reproduced alternative."

According to the Edmunton Journal, the 2012 Kia Optima is already there and "sounds and drives like regular sedan even when in EV mode." said Ford, however, doesn't think noisemakers are needed and the 2012 Ford Focus Electric will go on sale without any "pedestrian alert systems." But when legislation requires it, it will also sound like a regular noisy car. "We've finished a lot of research around what kinds of sounds are the most effective and least intrusive," Ford's Director of Electrification and Sustainable Mobility Programs, Sherif Markaby, told "In fact, we just finished a survey online with incredible response, and the sound that was far and away the highest rated was the one that sounded most like a combustion engine."

Meanwhile, carmakers continue efforts to make conventional combustion engine cars sound quieter. It is conceivable that someday in the not-to-distant future, hybrids could, by law, be noisier than new combustion engine cars. "If you listen to cars driving down the road, there's almost no way of knowing what kind of powertrain any of them have based on how quiet they are these days," Markaby told

The final rules on hybrid noisemakers will be in place by Jan. 2014, according to By Sept. 2017 all new hybrid and electric cars will sound like regular cars. They won't, however, require a person to walk in front of them with a flag.

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