Gas-electric hybrids, propelled by electric motors at low speeds, are well-known for their quiet ride and great mileage. But their silence isn’t always golden.

Some researchers and safety groups say that quiet operation can pose risks for unsuspecting pedestrians and the blind, who use sound cues.

Advocates for the blind have sought the addition of artificial noises in hybrids for several years, concerned that the expected sales growth of hybrids could lead to more pedestrian fatalities and injuries. Hybrids account for about 2 percent of new car sales each year, but auto companies are expected to boost production in advance of tougher fuel efficiency standards this decade.

“This is an example of too much of a good thing,’’ said John Pare, executive director for strategic initiatives with the National Federation of the Blind. “Cars got quieter, that was good. Suddenly they got to be so quiet that it added an element of danger.’’

Congress is heeding the warnings, adding sound performance requirements for hybrids and electric cars to an auto safety bill.

Automakers helped develop the proposal in Congress and are moving forward with new artificial sounds that will be emitted from electric cars and future hybrid models.