As discussed in the previous post, the presence of hybrid cars is increasing on America's roadways. People may be trying to spend less money on gas or to do their part to contribute to a greener society or both, but an unintended consequence of these hybrids is that they pose a danger to pedestrians, especially blind people who rely on the noise cars make to avoid being hit. Hybrids operate mostly on electricity when moving at slower speeds and so they operate quietly.

Currently, HEVs are only a small percentage of cars on the road, but that number is likely to grow significantly in the coming years. In addition to popular hybrid models like the Toyota Prius and the Ford Escape, several automakers have produced all-electric cars such as the Nissan Leaf and the Chevy Volt. In 2012, Ford, Toyota, Honda and Mitsubishi intend to produce all-electric car models. With more HEVs on the road, the problems associated with quiet cars are likely to increase.

To deal with this issue, Congress passed the Pedestrian Safety Enhancement Act in 2010. The law requires the NHTSA to issue federal standards for pedestrian safety sound systems on electric or hybrid cars. The law gives great latitude as to what sounds the car may make, and many automakers are currently experimenting with chirping and whirring sounds as a vehicle is turning or backing up. The NHTSA will publish final regulations in 2014.

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