A new proposal to the US legislature is to increase pedestrian safety by making the green cars of the future louder.

Although electric vehicles are regularly touted as the future of urban transportation thanks to their minimal environmental impact, several groups have expressed concern that they could pose a risk to pedestrians because of their near-silent operation.

Electric and hybrid vehicles currently emit a low "hum", which is easily drowned out by wind, cars, or other environmental noises.

In a world where road safety education often promotes the mantra "stop, look and listen", consumer safety advocates and organizations such as the National Federation of the Blind have argued for a "safe and acceptable" level of sound to be artificially produced.

Their calls are supported by recent research from the US National Highway Traffic Safety Administration (NHTSA) which showed that in certain situations electric or hybrid vehicles were twice as likely to be involved in collisions with pedestrians.

Last week, the powerful US auto industry backed a letter of support for legislation that would require the NHTSA to set minimum standards for an alert sound on electric vehicles.

"The National Federation of the Blind commends the automobile industry for its leadership on this issue and for its genuine concern for the safety of blind Americans, cyclists, runners, small children, and other pedestrians," said National Federation of the Blind President Dr. Marc Maurer.

Although producing the sound is unlikely to present a technical problem, the debate is likely to centre around what type of sound should be emitted and how loud it should be, especially given that the reduction of noise pollution is seen as one of the benefits of electric vehicles.

As electric vehicles become more commonplace, the type of noise is likely to be government mandated (banning, for instance, consumers adding their own sounds to their cars), although some visionaries have already offered their own ideas - in 2007 Japanese designer Yoshio Takaoka produced an electric vehicle that emitted the clip-clop sound of horses' hooves.

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