You might chalk another one up to the law of unintended consequences–while hybrids and electric vehicles may be better for the environment, they operate much more quietly than traditional gasoline-powered vehicles. According to the U.S. Department of Transportation’s National Highway Traffic Safety Administration (“NHTSA”), this has resulted in approximately 2,400 pedestrian injuries per year where pedestrians were unaware of the hybrid or electric vehicle’s presence. In response (and in accordance with the Pedestrian Safety Enhancement Act of 2010, which required NHTSA to develop a requirement for an “alert sound” for pedestrians to be emitted by electric and hybrid vehicles), NHTSA announced recently that all newly manufactured hybrid and electric light-duty vehicles must make audible noise when traveling in reverse or forward at speeds up to 19 miles per hour. (The sound alert is not required at higher speeds because tire and wind noise provide adequate audible warning to pedestrians.) The new federal standard, Federal Motor Vehicle Safety Standard No. 141, is available here.

Under the new standard, manufacturers have until Sept. 1, 2019, to equip all new hybrid and electric vehicles with the required sound alerts. According to NHTSA, the new requirement will help pedestrians who are blind, have low vision, and other pedestrians detect the presence, direction and location of hybrid and electric vehicles when they are traveling at low speeds. Indeed, the new standard was praised by both the American Council of the Blind and the National Federation of the Blind.

Under the final rule, each hybrid and electric vehicle must meet minimum sound requirements any time the vehicle’s propulsion system is activated, including when the vehicle is stationary (unless the vehicle’s gear selector is in the “park” position or the parking brake is applied). In addition, the sound must increase as the vehicle’s speed increases. And, unlike a traditional car horn, the alert sound must not require activation by the driver. Manufacturers are also prohibited from installing an “off switch” or volume control that would allow the driver to turn off or turn down the alert sound.

In connection with its announcement of minimum sound requirements for hybrid and electric vehicles, NHTSA also released its Final Environmental Assessment on the new standard. The Environmental Assessment examines various ways that manufacturers can comply with the new sound emission requirements and assesses their environmental impact. The Report concludes that “under the Preferred Alternative, noise impacts are anticipated to not be noticeable to humans, with the exception that in non-urban environments, single-vehicle pass-by events would be noticeable to humans at a distance of 7.5 meters from the source. In these infrequent occurrences, the anticipated noise levels would be below average [internal combustion engine] vehicle sound levels, and the perceived change would be comparable to existing ICE vehicle sound variation. Under Alternative 3, no noticeable impacts are anticipated due to the small sound level changes and the low percentage of vehicle hours of operation that potentially would be impacted by the minimum sound requirement.”