The first U.S. self-driving car fatality took place in May when the driver of a Tesla S sports car using the vehicle's "autopilot" automated driving system died in a collision with a truck in Florida, federal officials said Thursday.

The government is investigating the design and performance of Tesla's system.

Preliminary reports indicate the crash occurred when a tractor-trailer rig made a left turn in front of the Tesla at an intersection of a divided highway where there was no traffic light, the National Highway Traffic Safety Administration said. The Tesla driver died due to injuries sustained in the crash, which took place May 7 in Williston, Florida, the agency said. The city is southwest of Gainesville.

Tesla said on its website neither the driver nor the autopilot sensors noticed the white side of the trailer, which was perpendicular to the Model S, against the brightly lit sky, and neither applied the brakes.

"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," the company said. The windshield of the Model S collided with the bottom of the trailer.

The company said the accident led to the first kno