The new rule requires the generator to emit a noise whenever an EV or hybrid is idling, or travelling forward or in reverse at speeds up to 30km/h.
At speeds over than 30km/h, NHTSA reasons that the "sound alert is not required because other factors, such as tyre and wind noise, provide adequate audible warning to pedestrians".
According to NHTSA, the new rule, once fully implemented, is estimated to prevent 2400 pedestrian injuries per year in the States, although it may "not necessarily have an impact on those crashes involving pedestrian fatalities". That's because hybrids and EVs are involved in fewer pedestrian fatalities, and most pedestrian deaths involve vehicles travelling at speeds over 55km/h.
The agency estimates that the software and hardware required to comply with this rule will add around US$130 ($172) to the cost of a new hybrid, and US$55 ($73) to the cost of an EV. Some cars, such as the Nissan Leaf and Kia Soul EV, are already sold Stateside with noise generation equipment.
In announcing the new rule, Dr Mark Rosekind, NHTSA's Administrator, stated: "This is a common-sense tool to help pedestrians — especially folks who are blind or have low vision — make their way safely. With pedestrian fatalities on the rise, it is vitally important we take every action to protect the most vulnerable road users."
The new rule was release overnight by the United States' National Highway Traffic Safety Administration (NHTSA), and effectively gets the wheels in motion for enforcing a mandate, the Pedestrian Safety Enhancement Act, that was passed by Congress back in 2010.
Although the new rule comes into full effect from September 1, 2019, 50 per cent of each manufacturer's EV and hybrid production must be compliant by September 1, 2018.