Is that a Prius I hear approaching?

They may be heralded by their supporters as both unobtrusive and fuel efficient, but for blind and partially-sighted pedestrians the quiet nature of hybrid and all electric vehicles could have potentially tragic consequences.

Now researchers at car design specialist Lotus Engineering hope to have solved the problem with a new system that makes "quiet" hybrid vehicles sound like conventional cars.

The company has fitted a demonstration version of the technology to a Toyota Prius and claims that it provides realistic engine noises for pedestrians while having negligible impact on the driver.

The system works by monitoring the car's speed and broadcasting an appropriate "synthesised" engine sound through a waterproof speaker mounted on the radiator. The company claims the system is fully automated and uses recorded sounds from an existing engine so that it is instantly recognisable, allowing pedestrians to better judge speed and distance.

The work was welcomed by both the Guide Dogs for the Blind Association and campaigners for road safety.

"Blind and partially sighted people use the noise of oncoming traffic as a cue for when it is safe to cross a road – if a "quiet" hybrid electric vehicle is approaching then they will no longer have this cue and are immediately put at risk," explained Clive Wood, Transport Policy Officer at the charity. "The charity recognises the environmental benefits of these vehicles however more consideration needs to be given to the safety implications to visually impaired pedestrians."

Mike Kimberley, chief executive of Group Lotus, agreed that action should be taken to improve the safety credentials of hybrid and electric vehicles, adding that he hoped legislators would introduce minimum noise requirements for such cars.