Because they can be nearly silent, hybrid cars pose a serious threat of injury and death to blind and visually impaired people, says the American Council of the Blind, which is pushing the auto industry and government officials to develop ways to reduce this danger.

"Traditionally, people who are blind or visually impaired learn to rely on their hearing and tactile cues to provide them with information about their environment, which they can use to navigate safely across streets and through other vehicular ways, such as parking lots. In so doing, the sound of traffic is their primary focus," Melanie Brunson, council executive director, said in a news release from the council.

"Traffic sounds provide information about such things as the position of vehicles, their direction of travel, their rate of acceleration, and the speed at which they are likely to move. With this information, the pedestrian can make informed decisions about when to cross a street or other vehicular way safely," she said.

Without those sound cues, a blind or visually impaired person is at serious risk.