WASHINGTON - Advocates for the blind want the government to set minimum sound standards for new cars and trucks, pointing to potential safety hazards for blind pedestrians who can't hear silent gas-electric hybrid vehicles.

The National Highway Traffic Safety Administration held a daylong hearing yesterday to discuss the issue, which has been raised by organizations that represent about 1.1 million legally blind Americans. "For us, these cars are invisible," said Deborah Kent Stein of the National Federation of the Blind.

Stein and representatives of other organizations for the blind said hybrid vehicles are difficult for blind pedestrians to detect, since they use traffic sounds to determine when it's safe to cross the street. They asked the government to conduct more research into the issue and require cars to emit minimum decibel levels.

Industry officials said they hoped to begin preliminary testing later this year to quantify typical noise emissions from vehicles. But they said the issue is complicated because so many things contribute to traffic sounds: engines, tires hitting the road, wind resistance, and background noise.

"There are a lot of things that we simply don't know at this point," said Chris Tinto, a Toyota Motor Corp. vice president who is leading an industry panel reviewing the issue.

During the meeting, researchers played audio tapes comparing the sounds of hybrids with vehicles that have conventional engines. In one experiment, blindfolded listeners couldn't hear a 2006 Toyota Prius until it was about 11 feet away, compared with a 2004 Honda Accord, which the listeners detected from a distance of about 36 feet.

Some lawmakers are taking notice. US Representatives Ed Towns, a Democrat from New York, and Cliff Stearns, a Republican from Florida, introduced legislation in April that would require a two-year study of the issue by NHTSA.

Hybrid vehicles operate on battery-powered electric motors at low speeds and when idling, reducing the amount of sound from the vehicle compared with conventional cars and trucks.

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