BALTIMORE —  A bill intended to protect blind people and other pedestrians from the dangers posed by quiet cars will be introduced Wednesday in Congress.

The measure would require the Transportation Department to establish safety standards for hybrids and other vehicles that make little discernible noise, including an audible means for alerting people that cars are nearby.

"The beneficial trend toward more environmentally friendly vehicles has had the unintended effect of placing the blind and other pedestrians in danger," said Democratic Rep. Edolphus Towns, who's sponsoring the bill with Republican Rep. Cliff Stearns.

The Baltimore-based National Federation of the Blind has pushed for the legislation to protect those who rely on their hearing to know when to cross the street.

While the organization is not aware of people being struck by cars they couldn't hear, NFB President Marc Maurer has said he fears it's only a matter of time.

Preliminary results of an ongoing study at the University of California-Riverside have indicated the cars pose some risk. The study found that hybrids operating at slow speeds must be 40 percent closer to pedestrians than combustion-engine vehicles before they make enough noise for their location to be detected.

Hybrid vehicles operate on battery-powered electric motors when idling and traveling at slow speeds; internal combustion engines, with their distinctive rumble, kick in when the cars speed up.

The bill would require the Transportation Department to conduct a two-year study before issuing safety standards. Automakers would than have two years to comply.

The National Highway Traffic Safety Administration is planning a listening session this spring to consider possible solutions to the quiet-car problem and is already working with manufacturers.

Wade Newton, a spokesman for the Alliance of Automobile Manufacturers, said he couldn't comment on the bill's specifics but added that manufacturers were eager to address the issue.

Clarence Ditlow, president of the Center for Auto Safety, said he favored enhanced safety standards for quiet cars but wasn't sure a two-year study was necessary.

"It seems to me that if we can put audible signals on walk signs for the blind, then we can put an audible signal on a hybrid," Ditlow said.