The agency in February 2018 finalised rules requiring EVs and hybrids to emit alert sounds to warn pedestrians of their approach, extending to 2020 the deadline for full compliance.
The long-delayed rules, which were first demanded by Congress in 2010, require automakers like Tesla Inc, Nissan Motor Co and General Motors Co to add sounds to vehicles when they are moving at speeds of up to 30kph to help prevent injuries among pedestrians, cyclists and the blind.
The agency on Monday said in response to a petition from automakers it was proposing to amend its rules “to remove the current limitation of one sound per vehicle model.” The agency wants public comment “on whether there should be a limit to the number of compliant sounds that a manufacturer can install in a vehicle and what that limit should be.”
NHTSA required the alerts be in all “quiet” vehicles by September 2020. Automakers were required to have the sounds in 50% of vehicles by Sept 1.
To meet emissions requirements from California, automakers need to sell more electrically powered vehicles, and those vehicles are often harder to hear at lower speeds than gasoline-powered engines.
At higher speeds, tyre noise, wind resistance, and other factors eliminate the need for a separate alert sound, regulators say.
The Trump administration froze the Obama-era rule as it conducted a review of petitions from automakers. Nissan had argued that the alert was only needed up to 20kph.
NHTSA said last year it expects the rules finalised on Monday to prevent 2,400 injuries annually by 2020 and to require the addition of alert sounds to about 530,000 model 2020 vehicles.
NHTSA has said the rules will cost the auto industry about US$40 million annually because automakers will need to add an external waterproof speaker to comply. But the benefits of the reduced injuries are estimated at US$250 million to US$320 million annually.
The agency estimates the odds of a hybrid vehicle being involved in a pedestrian crash are 19 percent higher than with a traditional gasoline-powered vehicle. About 125,000 pedestrians and cyclists are injured annually on roads in the United States.