Automakers agree to put automatic braking in cars by 2022

The voluntary agreement with 20 car manufacturers means that the important safety technology will be available more quickly than if the government had gone through the lengthy process of issuing mandatory rules, said Mark Rosekind, head of the National Highway Traffic Safety Administration.

But some safety advocates have filed a petition asking the government to issue mandatory regulations, saying the voluntary agreements aren't enforceable.

Automatic braking systems use cameras, radar and other sensors to see objects that are in the way, and slow or stop a vehicle if the driver doesn't react. It's the most important safety technology currently available that's not already required in cars.

Many automakers already offer automatic braking, but it is most often part of an options package available on high-end vehicles that consumers have to pay extra to get.

"A commitment of this magnitude is unprecedented, and it will bring more safety to more Americans sooner," Rosekind said.

Deborah Hersman, president of the National Safety Council, said the agreement "has the potential to save more lives than almost anything else we can accomplish in the next six years."

There are about 1.7 million rear-end crashes a year in the U.S., killing more than 200 people, injuring 400,000 others and costing about $47 billion annually. More than half of those crashes could be avoided or mitigated by automatic braking or systems that warn drivers of an impending collision, NHTSA has estimated.