The NHTSA Says Electric Vehicles Can No Longer Stay Silent at Low Speeds

A new ruling mandates that, by 2019, electric and hybrid cars must emit artificial sounds so pedestrians, cyclists, and the blind can better detect these ultraquiet machines. It codifies the Pedestrian Safety Enhancement Act that Congress passed in 2010, with support from engineering group SAE International and various industry and advocacy groups for the blind. The feds first raised the issue back in 2007, well before the second-generation Toyota Prius would push hybrids into the mainstream.

The National Highway Traffic Safety Administration (NHTSA) estimates the added noise will prevent 2400 pedestrian injuries each year after September 1, 2020, when every new hybrid and EV must be equipped to make sounds. Automakers must equip at least half of such models by September 2019. Only vehicles under 10,000 pounds GVWR are included; electrified motorcycles, three-wheelers, and medium- and heavy-duty trucks are exempt. Want more logic? Gasoline and diesel vehicles with auto stop/start systems aren’t required to make extra sounds while stationary, while EVs and hybrids must.

NHTSA will require automakers to install external speakers that emit simple tones whenever the car is stationary, in reverse, or traveling up to 19 mph (30 km/h was used as the cutoff). By “simple,” we mean that NHTSA doesn’t want automakers replicating the sounds of internal-combustion engines. Rather, they’re calling for two or four tones between 315 and 5000 hertz, separated in one-third-octave intervals.

Volume must also increase by three decibels with each 6-mph increase in speed. Under electric power, these cars must emit between 47 and 67 decibels (the decibel curve as calibrated with an A contour, which best replicates how the human ear perceives differences in sound intensity).

For those concerned with noise pollution and the mating habits of tree squirrels—for real, NHTSA conducted a wildlife analysis—fear not. The agency claims that if hybrids and EVs reach 50 percent of all registered vehicles by 2035—a highly unlikely scenario even by polling-institute standards—such sounds would increase ambient noise in urban and nonurban areas by less than 1 decibel each. “Differences in sound levels of less than 3 decibels are generally not noticeable to humans,” the agency said.

When compared against ambient noise in cities (factored at 55 decibels), EVs will sound only 1.1 to 2.7 decibels louder than the surrounding environment. This would seem to contradict what the agency just said above, except the “increase is nonetheless expected to make the vehicles more detectable to intent listeners using vehicle sound to guide roadway crossing.” Outside city centers, where 35 decibels is considered to be the average ambient-noise level, a new EV or hybrid would be 3.5 to 6.6 decibels louder (and 10.4 decibels louder when stopped). NHTSA also points out that the sounds will be 0.3 t0 4.4 decibels quieter than a car relying only on internal combustion.