New hybrid and electric cars must make noise while driving slowly, new U.S. rule says

New hybrid and electric cars must make noise while driving slowly, new U.S. rule says - LA Times: "
New hybrid and electric cars are required to make noise when traveling at low speeds so that pedestrians, especially those who are blind or have poor eyesight, will hear them coming, under a new rule released Monday by the Obama administration.
The new rule could help prevent about 2,400 pedestrian injuries a year once all hybrids on the road are equipped to make noise, according to the National Highway Traffic Safety Administration.
Hybrid vehicles use both a gasoline engine and an electric motor.
Electric motors, however, make very little noise compared with gasoline and diesel engines.
The rule requires hybrid and electric vehicles to make audible noise when traveling in reverse or forward at speeds up to about 19 mph. 
The sound alert isn't required at higher speeds because other factors, such as tire and wind noise, provide a warning..."