To Avoid Blindsiding Pedestrians, EVs may be Required to be Noisier

There are places where quiet is strictly enforced, like the library and the ballet, but a certain decibel level soon will be required from all vehicles on city streets, in compliance with a law passed by the U.S. Congress late last year and signed by President Barack Obama in January.

In Washington, D.C., the National Highway Traffic Safety Administration (NHTSA) announced on July 7  that the agency is taking the first major step toward proposing regulations that will protect unwary pedestrians and the visually-impaired from accidents involving hybrid and electric vehicles. In addition to HEVs and EVs, the regulations will cover light and low-speed vehicles, motorcycles, buses, and heavy-duty trucks, according to USA Today.

The action is mandated by the Pedestrian Safety Enhancement Act of 2010, a bill to establish a motor vehicle safety standard that provides for a means of alerting blind and other pedestrians to motor vehicle operation.

“Even as we make giant leaps forward with hybrid and electric vehicles, we must remain laser focused on safety," said NHTSA Administrator David Strickland.  "With more and more quiet vehicles on the road, we have to consider their effect on pedestrians."

The legislation was, in part, the result of a study led by perceptual psychologist Lawrence Rosenblum of the University of California, Riverside. The researchers, featured in Scientific American magazine in August 2008, blindfolded subjects, who then were asked to listen to recordings of cars approaching at five miles per hour. The subjects could locate the familiar hum of a Honda Accord’s internal-combustion engine 36 feet away. But they failed to identify a Prius, running in electric mode, until it came within 11 feet—giving them less than two seconds to react before the vehicle reached them. And that was in the absence of traffic noise or other distractions.

However, recent studies from Western Michigan University indicate that hybrids and conventional vehicles are equally safe when traveling more than about 20 miles per hour, because tire and wind noise generate most of the audible cues at those speeds. Hybrids also tested safe when leaving a stoplight; all Prius models in the study engaged their internal-combustion engines when accelerating from a standstill.

NHSTA first held a public forum about pedestrian safety risks posed by hybrids and EVs in 2008. In a 2009 report, it found a higher rate of pedestrian accidents associated with hybrid vehicles than with gasoline vehicles. An April 2010 report determined that such quiet cars, when running on electric motors only, were a safety risk to visually impaired walkers

Adding noise to hybrids may be unavoidable, but at least it won’t have to be earsplitting, Rosenblum says. That human brain is much more sensitivity to approaching sounds—because they are more likely to pose a threat— than to those that are fixed or moving away. As long as a car makes the right kind of sound, it can be subtle. Chirps, beeps and alarms are more distracting than useful, say Rosenblum and Everett Meyer of Enhanced Vehicle Acoustics in Santa Clara, Calif.; the best sounds for alerting pedestrians would be carlike—akin to the soft purr of an engine or the slow roll of tires across pavement.

Even with sound-emitting safety measures in the works, Robert S Wall Emerson of Western Michigan University, Kalamazoo ,  predicts a future of more tranquil transportation. Several gas-powered motor vehicles are already quieter than hybrids, he says. In fact, in some of his most recent studies, hybrid SUVs turned up noisier than many luxe internal-combustion vehicles.