WASHINGTON -- A driver killed in the May 7 crash of a Tesla Motors Inc. car while using Autopilot driving-assist software was speeding, U.S. highway safety investigators said on Tuesday in a preliminary report that did not state a probable cause.
The U.S. National Transportation Safety Board (NTSB) said its preliminary findings showed the Model S was traveling at 74 mph in a 65-mph zone at the time it struck a semi-truck near Williston, Fla.
Joshua Brown was killed when his vehicle drove under the tractor trailer. It was the first known fatality involving a Model S operating on the Autopilot system that takes control of steering and braking in certain conditions. The accident increased scrutiny of automated driving technology.
The report said the NTSB confirmed the Model S driver was using the advanced driver assistance features Traffic-Aware Cruise Control and Autosteer lane-keeping assistance at the time. The NTSB has not yet determined the probable cause of the crash.
Tesla did not immediately respond to a request for comment. Tesla CEO Elon Musk has repeatedly said the company has no plans to disable the feature.
Speeding alone would not be considered the cause of a vehicle crash, but could be a contributing factor, said NTSB spokesman Christopher O'Neil.
"All aspects of the accident remain under investigation," O'Neil said, adding that the agency will typically release a final report about a year after the preliminary report.
A lawyer for the Brown family, Jack Landskroner, said in an email on Tuesday that the findings were preliminary and that the investigation was ongoing.
A Florida Highway Patrol investigation is continuing and the police force has no plans to criminally charge the truck driver, Sergeant Kim Montes said Tuesday.
She said the police force is still considering whether to issue a traffic citation to the truck driver for failing to yield. A lawyer for the truck driver did not immediately respond to a request for comment on Tuesday.
The NTSB report said the force of the initial impact of the crash resulted in the battery disengaging from the electric motors powering the car. After exiting from underneath the truck, the car traveled 297 feet, then collided with a utility pole. The car broke the pole and traveled an additional 50 feet.
Tesla faces a separate investigation by the U.S. National Highway Traffic Safety Administration into whether the system poses an unreasonable risk to driver safety.
The NHTSA also wants to know what Tesla investigators have learned about the crash. On July 8, that agency sent a nine-page letter to Tesla requiring the Palo Alto, Calif.-based automaker to file responses in the coming weeks.