After years of trying to make cars sound as if they were riding on air, engineers are considering how they might make them noisier. They’re trying to make hybrids and electric cars more audible to pedestrians.

A team of engineers developing the Leaf, the forthcoming electric car from Nissan, has been presenting ideas for artificial noises to government officials and focus groups, such as a chiming sound, a melody or perhaps a futuristic whirring inspired by the flying cars in “Blade Runner.”

As hybrids proliferate and major automakers such as Nissan and General Motors prepare to launch electric vehicles next year, some automakers are seeking to address concerns in the U.S. and Japan that the nearly noiseless vehicles might be so quiet that they pose a threat to pedestrians.

At a meeting this month, Nissan presented its chime and other sounds to the National Highway Traffic Safety Administration.

Regulatory committees in the United States and Japan are also studying complaints about the cars, and Congress is weighing a measure requiring vehicles to issue “non visual” warnings to pedestrians.

But the industry is divided over whether safety sounds should be added to the quiet cars and, if so, what those noises should be. “Frankly, we’ve been working for 30 years to make cars quiet — never thinking they could become too quiet,” said Robert Strassburger, vice president for vehicle safety at the Alliance of Automobile Manufacturers, an industry group. But now “those vehicles may be difficult to detect.”

Hybrid vehicles typically operate on hushed battery-powered electric motors when idling and traveling at low speeds. At higher speeds, the noisier internal combustion engine kicks in on hybrids. Toyota, maker of the popular hybrid Prius, which runs very quietly at low speeds, doesn’t add artificial sounds.

Cars such as Nissan’s Leaf, Tesla’s Roadster and General Motors’ Volt, which will depend on battery electric power, might be even quieter. At higher speeds, the rush of air and rumble of tires can make electric vehicles almost as noisy as gas-powered cars.

Officials at Tesla say they have no plans for “fake noises.” The company already makes the $109,000 electric Roadster, a luxury car popular with eco-conscious celebrities.
“We have delivered more than 700 cars, and our customers overwhelmingly say the relative quiet of the power train is one of the most appealing aspects of the car,” said Tesla spokeswoman Rachel Konrad. “Thanks to widespread electric vehicle adoption, we will all enjoy far less noise pollution in the future.”

Evidence that hybrids pose a safety threat has been scant, in part because they are new and represent only a small fraction of the more than 230 million vehicles on the road, transportation officials said.

But a not-yet-released traffic safety administration study of accidents in 12 states compares accident rates for some hybrid vehicles and other vehicles.

Covering more than 8,000 hybrid electric vehicles and nearly 600,000 regular cars, the analysis suggests that during certain low-speed maneuvers such as turning and backing up, hybrids are 50 percent more likely to be involved in an accident with a pedestrian, said Ronald Medford, an acting deputy administrator at the traffic safety agency.

“We certainly know that blind pedestrians rely heavily on the sound of vehicles as a means of determining when it is safe to cross the road,” he said. “But all of us are susceptible.”

Rep. Edolphus Towns, D-N.Y., has introduced a bill that would require the Transportation Department to establish a safety standard under which cars would have to be equipped to issue “nonvisual alerts.”

It has garnered 139 sponsors, among them. Rep. Cliff Stearns, R-Fla., who says he has been startled by a quiet car.

“I was … in the parking lot of a shopping center, and I was wheeling my groceries with my wife, and Ididn’t hear a car come up behind me,” Stearns told reporters. “If all the cars are silent in the future, it does pose a problem.”

But there is little agreement over what the sound should be, how loud it ought to be and whether manufacturers should be allowed to create their own distinctive audio tracks:
The Fisker Karma, a luxury electric vehicle, will have an integrated audio system that will alert pedestrians and give the car a “distinctive audio signature” that will be “reflective of the car’s advanced technology,” a spokes man said.

Officials with the National Federation of the Blind, which has pressed the safety issue with automakers and regulators, have recommended the electric cars make sounds similar to those of gas-powered cars.

“Society is conditioned to that sound,” said John Pare, director of strategic initiatives for the group.

There is some concern that if variety of noises are permitted then electric cars could merely add another layer to the urban cacophony potentially conflicting with state and local laws governing decibel levels.

“If we all do it differently, we will confuse the heck out of the consumer,”‘ said Nancy Gioia, director of hybrid and sustainable technology at Ford.