WASHINGTON (Reuters) - The Trump administration said Monday it will drop rules first proposed in 2012 that would have required automakers to install brake-throttle override systems to prevent runaway vehicles.

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The regulation was proposed by the National Highway Traffic Safety Administration (NHTSA) in response to a series of unintended sudden acceleration incidents in Toyota Motor Corp vehicles. It would have required that all motor vehicles’ brakes be able to override the accelerator pedal.

The proposal was aimed at ensuring the driver could halt a vehicle by applying the brakes if a throttle pedal was trapped by a floor mat, shoe or other obstruction.

In 2012, NHTSA said some automakers had not yet made the systems standard. On Monday NHTSA said all automakers have voluntarily installed brake throttle override systems on all new vehicles and the agency does not anticipate any automakers removing the system.

But in dropping the proposed rule, NHTSA will not set braking distance requirements for the systems and other performance requirements.

Gloria Bergquist, a spokeswoman for the Alliance of Automobile Manufacturers, a trade group representing General Motors Co, Toyota, Volkswagen AG and others, said the rule was no longer necessary.

“When the technology is in widespread use now, there is no need to continue a rulemaking,” she said.

Brake throttle override systems work by the vehicle software cutting power to the throttle if both pedals are depressed.

NHTSA had also proposed extending its rules to require vehicles to return to idle when a driver stops pressing on the accelerator pedal or in response to a “failsafe operation” to include electronic throttle control systems.

On Monday, NHTSA said a “broader understanding of safe design of vehicle electronic control systems is needed to make an informed decision on regulating return-to-idle.”

It said there were “substantial challenges” in designing objective tests for the operation of brake throttle override systems.

The agency in 2012 cited the August 2009 sudden acceleration crash that killed four people when a California Highway Patrol officer was driving a loaner Lexus ES350 that had the wrong floor mat installed.

Toyota recalled more than 10 million vehicles worldwide because of unintended acceleration issues in 2009 and 2010. Several government reviews found no evidence that electronic glitches were to blame for unintended acceleration — but blamed the issues on mechanical interference like floor mats.

In 2014, Toyota paid a $1.2 billion Justice Department fine after it admitted it misled U.S. consumers by concealing and making deceptive statements about the extent of sudden acceleration problems.