Electric and hybrid vehicles are quiet … too quiet, according to the US Department of Transportation. Although the unobtrusive thrum of an EV in motion could be thought of as a positive thing, the Department's National Highway Traffic Safety Administration (NHTSA) has announced a new safety standard that will require newly-manufactured hybrid and electric vehicles to emit artificial warning sounds to alert pedestrians to their presence.

The new rule is the product of the Pedestrian Safety Enhancement Act 2010, and the process of defining the specifics has been caught up in the bureaucratic process for years. Now that it's official, the new Federal Motor Vehicle Safety Standard No. 141 will help prevent around 2,400 pedestrian injuries per year, according to the NHTSA. The European Commission and the UN are both already considering similar regulations.

Applying to all hybrid and electric light-duty vehicles with four wheels and a gross weight of 10,000 lb (4,536 kg) or less, the new standard states that these vehicles will be required to emit an audible noise while running, both forwards and in reverse, below 18.6 mph (30 km/h). Any faster than that, and noise from the wind and wheels are apparently loud enough to alert any nearby pedestrians or cyclists to the vehicle's presence.

"We all depend on our senses to alert us to possible danger," says Anthony Foxx, US Transportation Secretary. "With more, quieter hybrid and electrical cars on the road, the ability for all pedestrians to hear as well as see the cars becomes an important factor of reducing the risk of possible crashes and improving safety."

September 1, 2018 is the first deadline, when at least half of newly-manufactured hybrid and electric vehicles must be fitted with these systems. After that, manufacturers will have exactly one year to ensure that their entire fleets meet the requirements.