One of the distinct benefits of electric automobiles -- the quiet ride -- is about to disappear. The National Highway Traffic Safety Administration (NHTSA) last week rejected requests to reconsider new rules requiring hybrid and electric vehicles to make more noise while moving, or while stopped at traffic lights. In 2011, President Obama signed a bill directing the agency to come up with details for how to implement the idea.

"This landmark legislation requires electric and hybrid car manufacturers to add sounds to alert all pedestrians to the presence of these unusually quiet vehicles," Obama said at the time. "These provisions will help increase the safety and independence of blind and visually impaired Americans."

Studies show that hybrid cars are 18 percent more likely to slam into pedestrians and 51 percent more likely to strike bicyclists compared to conventional, gas-powered alternatives. So NHTSA followed the lead of the European Union which adopted similar, but not identical noise requirements.

The newly updated US rule mandates that half of all quiet cars manufactured after September 1, 2019 start making noise any time the vehicle transmission is not in park. The noise would only shut off after the car travels faster than 19 MPH. All electrics and hybrids must comply by 2020, and manufacturer will have to document compliance with regular reports. NHTSA estimates manufacturers will spend $42 million to satisfy the new requirements, a figure manufacturers say is far too low.

Manufacturers must ensure that the noisemaking device cannot be defeated or removed. Local governments would not be affected because big, electric-powered municipal buses are exempt from the noise requirement. Manufacturers will have only a limited amount of control over how their cars sound.

"The safety standard allows manufacturers to provide each vehicle with one or more alert sounds that comply, at the time of manufacture, with the safety standard," the final rule states. "Thus, a manufacturer may, if it so chooses, equip a vehicle with different sounds to denote different operating scenarios, such as stationary, forward or reverse."

The agency noted that "for the time being" the rules do not apply to gasoline-engine cars, but NHTSA did not rule out expanding the regulation to require noisemakers on conventional vehicles.