Although there are many environmental and financial benefits to hybrid and electric vehicles, there may also be added risks as a result of their lack of traditional gas-engine noise. Federal data indicates that pedestrians and bicyclists are more likely to be injured in a pedestrian accident involving a hybrid or electric as they are with traditional gas-powered vehicles.

According to a 2009 study completed by the National Highway Traffic Safety Administration (NHTSA), hybrid cars were twice as likely to be involved in an auto-pedestrian accident as standard vehicles. As a result of that study, the Pedestrian Safety Enhancement Act became law in 2010. The act requires that the NHTSA develop and implement federal standards for a sound system on hybrid and electric vehicles. The agency has projected that it will release those standards in 2014.

The pedestrian safety act does not instruct automakers to include any specific sound in hybrid or electric vehicles, but it does set a minimum sound standard and requires that drivers not be able to deactivate the sounds.

Some groups and individuals have opposed the act, saying that it would unnecessarily contribute to noise pollution. Opponents claim that there has not yet been a comprehensive study measuring the potential danger posed by hybrid and electric vehicles to pedestrians and bicyclists.

However, the National Federation for the Blind is among the groups supporting the law, stating that noise is essential for the safety of vision-impaired pedestrians. "Blind people simply cannot travel safely and independently without hearing vehicle sounds," said Federation spokesperson Chris Danielson.

Source: MSN Money, "Hybrids: Quiet threat to pedestrians," Mark Vallet, Oct. 11, 2011