Tesla said Thursday a driver was killed while using its self-driving mechanism on a Model S electric car, leading to a federal safety investigation.
Tesla said the National Highway Traffic Safety Administration (NHTSA) had opened a "preliminary evaluation" into the performance of autopilot after the electric car company notified the agency of the fatality.
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In a statement, Tesla said the fatality was "a tragic loss" and was the first such incident with its autopilot system activated.
"This is the first known fatality in just over 130 million miles (209 million kilometers) where autopilot was activated," the company said.
"Among all vehicles in the US, there is a fatality every 94 million miles. Worldwide, there is a fatality approximately every 60 million miles," it said.
"It is important to emphasize that the NHTSA action is simply a preliminary evaluation to determine whether the system worked according to expectations."
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Tesla, known for its high-end electric cars, unveiled the system last year which allows the vehicle to automatically change lanes, manage speed and even hit the brakes. The system is activated and overridden by the driver.
Tesla said that in the fatal accident, the car was on a divided highway when a tractor-trailer drove across the road to be situated perpendicular to the Tesla.
"Neither autopilot nor the driver noticed the white side of the tractor-trailer against a brightly lit sky, so the brake was not applied," the statement said.
"The high ride height of the trailer combined with its positioning across the road and the extremely rare circumstances of the impact caused the Model S to pass under the trailer, with the bottom of the trailer impacting the windshield of the Model S."
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