WASHINGTON — Common wisdom holds that an automobile's piston engine can purr, rattle or — particularly in the movies — explode.
While the U.S. secretary of transportation would rather your engine do the former than the latter, he believes that a car in motion ought to make enough noise to be noticed.
"This proposal will help keep everyone using our nation's streets and roadways safe, whether they are motorists, bicyclists or pedestrians, and especially the blind and visually impaired," Transportation Secretary Ray LaHood said.
He is worried that electric and hybrid vehicles can sneak up on people without warning, putting walkers and bikers at risk. He endorsed a proposal from the National Highway Traffic Safety Administration that would require vehicles capable of moving in stealth to make enough noise so that people can sense them coming.
LaHood, who walks when he can and likes to ride his bicycle, joined a conversation among pedestrian and cycling advocates this week.
"I've heard that talked about at conferences in the past, but I haven't seen any evidence of it here yet," said Jim Sebastian, who coordinates the District of Columbia's bicycle programs.
Vigorous efforts to make Washington a safe city for walking and bicycling have contributed to a sharp reduction in overall traffic fatalities in the past decade, but eight of the 19 people who were killed in 2012 were pedestrians. Two of those deaths were hit-and-run accidents, but none appeared to involve a hybrid electric vehicle.
John Townsend II of AAA Mid-Atlantic sees an "ongoing concern" with quiet cars.
"Even if you're not wearing ear buds as you cross the street, you can be deep in your thoughts, and it's easy to walk in front of a car that you can't hear approaching," he said.
The sound of rubber meeting the road generally can be heard when a vehicle is moving above 18 mph, but federal research found that battery-powered cars were less likely to be heard at lower speeds. For example, hybrid electric vehicles were twice as likely to be in a pedestrian crash when the vehicle was backing out.
After hearing from pedestrian advocates, particularly those who seek to protect the interests of the blind, Congress ordered NHTSA to come up with guidelines.
The federal agency said it would leave it to auto manufacturers to figure out how to make the vehicles more noisy, but it said the noise must be loud enough to be heard amid a wide range of street noises and other background sounds. Vehicles of the same make and model would have to make the same sound or set of sounds, and those sounds would need to meet certain minimum requirements.
"Our proposal would allow manufacturers the flexibility to design different sounds for different makes and models while still providing an opportunity for pedestrians, bicyclists and the visually impaired to detect and recognize a vehicle and make a decision about whether it is safe to cross the street," said NHTSA Administrator David Strickland.
Statistics on national traffic fatalities take several months to compile after the end of each year, but preliminary data on the first nine months of 2012 indicate that deaths rose sharply after six years of steady decline.
The 7.1 percent increase was the biggest jump during the January-through-September time span since 1975, when federal officials began compiling traffic-death data. The increase, however, was in comparison to deaths in 2011, when they reached an all-time low.