Narrator: This is Science Today. If you've ever been in a hybrid car, you may have appreciated how quiet the engine runs when operating with their electric motors. But a University of California, Riverside study has found that this low audibility actually poses a risk to the blind. Lawrence Rosenblum, a professor of cognitive psychology, who led the study, has conducted previous research on visual and auditory perceptions of approaching cars.

Rosenblum: Folks at the National Federation of the Blind had been in contact with me because they've been concerned about the audibility of hybrid cars. Without that sound the blind in particular often have trouble judging the presence and position and speed of cars.

Narrator: Rosenblum found that hybrid cars approaching at a slow speed were virtually inaudible until they were just seven feet away - leaving a pedestrian only one second to react.

Rosenblum: There's currently a Congressional bill that's been proposed to determine whether maybe having minimum audibility for cars would be a good idea to institute in the next two to four years.

Narrator: For Science Today, I'm Larissa Branin.