Electric and hybrid vehicles which run so quietly they are practically silent pose a safety risk for blind and partially sighted people, a charity has warned.
The Guide Dogs charity said this may be a particular problem at pedestrian crossings where there are no visual and audible warnings to indicate it is safe to proceed.
Traffic sounds help people with visual impairment decide whether or not it is safe to cross a road, but with low-noise electric vehicles this assessment becomes very difficult, the charity said.
Guide Dogs' access and inclusion manager Carol Thomas said: "We recognise the environmental benefits of electric and hybrid vehicles. However they are virtually silent, and blind and partially sighted people rely on vehicle sound to assist with their mobility and orientation.
"This is particularly important when crossing roads, especially when there are no controlled pedestrian crossings with audible and tactile indicators. The sound of oncoming traffic, or absence of this sound, is used to assess when it is safe to cross the road.
"It is also helpful to blind or partially sighted people to know when vehicles are waiting at traffic lights. If a hybrid vehicle is stationary at a pedestrian crossing, it may not be heard but may be about to move."
A report by TRL - the Transport Research Laboratory - into accidents between pedestrians and quiet vehicles is due out soon.
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