Tesla Motors acknowledged today that a driver of one of its Model S cars operating in Autopilot mode died when the semi-autonomous system failed to detect a tractor-trailer turning in front of the luxury electric car.

The National Highway Traffic Safety Administration has begun a preliminary investigation of the fatal accident that occurred May 7 in Williston, Fla.

The case illustrates the experimental nature of autonomous vehicle technology that has attracted billions of dollars of investment from the auto and technology industries.

“This is the first known fatality in just over 130 million miles where Autopilot was activated,” states a post on Tesla’s corporate website. “Among all vehicles in the U.S., there is a fatality every 94 million miles. Worldwide, there is a fatality approximately every 60 million miles. It is important to emphasize that the NHTSA action is simply a preliminary evaluation to determine whether the system worked according to expectations.”

The post continues in substantial detail to describe the incident.

“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 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.”

In a statement, NHTSA said the beginning of a preliminary investigation “should not be construed as a finding that” the agency “believes there is either a presence or absence of a defect in the subject vehicles.”

Tesla’s Autopilot enables the vehicle to drive itself under most highway circumstances, but there are situations where drivers must be prepared to reclaim control. It is not clear whether the driver was alerted in this particular case.

General Motors is working on a system called Super Cruise that it previously said would be introduced next year to give the Cadillac CT6 “hands-free” driving, but the driver must remain engaged.

Earlier this month there was an incident in Irvine, Calif., where the owner of a brand new Tesla Model X, also equipped with Autopilot, accelerated from a parking space and crashed into a commercial building. The owner and Tesla disputed whether Autopilot specifically caused the unintended acceleration.

The message on Tesla’s website reflects legal advice about the limits of Autopilot’s capability.

“It is important to note that Tesla disables Autopilot by default and requires explicit acknowledgement that the system is new technology and still in a public beta phase before it can be enabled.

“When drivers activate Autopilot, the acknowledgment box explains, among other things, that Autopilot is an assist feature that requires you to keep your hands on the steering wheel at all times,¬†and that you need to maintain control and responsibility for your vehicle¬†while using it.”

Contact Greg Gardner: (313) 222-8762 or ggardner@freepress.com. Follow him on Twitter @GregGardner12

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