A measure calling for a study into the potential dangers hybrid cars pose to blind and other pedestrians because they are so quiet was introduced Wednesday in the U.S. Congress.

The bill, sponsored by Democratic Rep. Edophus Towns and Republican Rep. Cliff Stearns, seeks a two-year study from the Transportation Department on how to better protect pedestrians.

"The beneficial trend toward more environmentally friendly vehicles has had the unintended effect of placing the blind and other pedestrians in danger," Towns said.

Hybrid cars boost fuel efficiency by using a combination of a combustion engine and an electric motor. When cruising at lower speeds, the cars rely on the electric motor, which makes less noise.

In March, a University of California, Riverside study suggested hybrid cars running at low speeds fail to generate enough tire and aerodynamic noise to be heard.

Researcher Lawrence Rosenblum said hybrid cars relying on their electric motors must be 40 per cent closer to pedestrians than combustion-engine cars before they can be heard. The study was funded by the advocacy group the National Federation of the Blind.

The U.S. National Highway Traffic Safety Administration says it is examining the issue and is working with manufacturers to develop possible solutions.

In Canada, the Alliance for Equality of Blind Canadians has also said hybrid vehicles pose a safety threat to blind pedestrians. The group has called for alert systems including requiring hybrid cars to be equipped with silent radio transponders which would trigger a receiver carried by visually challenged pedestrians.

With files from the Associated Press