Image: Toyota Prius hybrid © Justin Sullivan, Getty Images

Taking a walk? Watch out for hybrids.

At low speeds, they move primarily by means of electricity, without the exhaust rumble and gear whine that have for 100 years signaled the approach of an internal-combustion engine. The result? Bicyclists and pedestrians are injured twice as often by hybrids, the National Highway Transportation Safety Administration says (.pdf file).

Of course, hybrids make up only a small percentage of vehicles on the road, and the toll on pedestrians from traditional cars is already huge.

In 2009, the most recent year for which there is data, vehicles struck and killed 4,092 pedestrians. An additional 50,000 or so are injured each year. A San Francisco trauma expert estimates that the medical costs for a pedestrian injured by a car in that city run about $80,000 per incident -- well above the minimum required car insurance liability coverage in every state.

But the crunch is about to get worse. As federal mileage rules take effect, dozens of silent mainstream models are on the way.

Peering into a future chock-full of hybrids and electric cars, NHTSA has proposed rules that will require electric vehicles and hybrid electric vehicles to emit sounds when moving at slow speeds. It did not, however, specify what kind of noise they should make.

Should they beep like a garbage truck in reverse? Make a fake engine sound? Automakers have been turning to Hollywood sound studios and Facebook to help make their decisions.

Electric vehicles are ramping up

If you think overly quiet electric cars are a problem for your grandchildren to solve, think again: 2012 is expected to be a game-changer.

Already, Toyota has put nearly 1 million of its Prius hybrids on U.S. roads, all capable of driving for short distances on electricity alone. Hybrid Ford Escapes are a favored taxicab in New York, and Lincoln's MKZ hybrid sells as well as its gas-only counterpart.

But pure electric vehicles have begun making inroads as well.

The all-electric Nissan Leaf has been the biggest plug-in seller in 2011. In the first seven months of the year, Nissan sold 4,806 Leafs. Its main competitor, the Chevy Volt (which carries a gas engine to recharge its batteries), sold 2,870 units. Tesla has delivered 1,000 of its high-priced Roadster models. In addition:

  • Ford promises an all-electric version of its Focus late this year.
  • Toyota will launch a RAV-4 electric vehicle as well as a plug-in version of its Prius.
  • Honda will offer a plug-in hybrid as well as a pure electric car.
  • Mitsubishi will launch an electric vehicle in 2012.
  • Luxury automaker BMW will lease 700 electric cars as a test project.

By some estimates, there will be more than 100 electric vehicles competing for market share in 2012, and the number of models is predicted to grow dramatically in the next decade. Accenture is forecasting 1.5 million electric vehicles on the road by 2015, with 10 million possible by 2020.

Fighting over the noise

A 2009 study by NHTSA found that in certain situations, hybrid vehicles were twice as likely to be involved in a pedestrian crash as traditional vehicles. In 2010, the Pedestrian Safety Enhancement Act was signed into law, requiring NHTSA to issue federal standards for a pedestrian safety sound system on electric cars. In July, NHTSA began looking for input. It's expected to publish a final rule in 2014.

Advocacy groups such as the National Federation for the Blind have pushed for changes to electric cars since the 2009 report was released. "Blind people simply cannot travel safely and independently without hearing vehicle sounds," says spokesman Chris Danielsen. "We use the sound of traffic to determine the speed and direction cars are moving as well as if they are accelerating or decelerating."

But a number of anti-noise-pollution groups have opposed the legislation, claiming that adding more noise to an already noisy environment will not help anyone.

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Their main argument lies in the fact that a comprehensive study has yet to be done. The 2009 NHTSA report sampled a very small segment of vehicles and the results were not conclusive. Richard Tur, the founder of NoiseOFF.org, argues, "The statistical difference only exists when EVs (electric vehicles) are backing up or making a slow turn. When going straight, the difference between EVs and ICE (internal combustion engine) vehicles disappears."

Mark Larsen of Utah State University examined fatality records, assuming that if electric and hybrids presented a real danger, pedestrian deaths would have risen since 2000, when hybrids first hit the market. The data showed pedestrian deaths fell over the observed time frame.