At 4:36 p.m. eastern daylight time on Saturday, May 7, 2016, a 2015 Tesla Model S 70D car, traveling eastbound on US Highway 27A (US-27A), west of Williston, Florida, struck a refrigerated semitrailer powered by a 2014 Freightliner Cascadia truck-tractor. At the time of the collision, the truck was making a left turn from westbound US-27A across the two eastbound travel lanes onto NE 140th Court, a local paved road. The car struck the right side of the semitrailer, crossed underneath it, and then went off the right roadside at a shallow angle. The impact with the underside of the semitrailer sheared off the roof of the car.

After leaving the roadway, the car continued through a drainage culvert and two wire fences. It then struck and broke a utility pole, rotated counterclockwise, and came to rest perpendicular to the highway in the front yard of a private residence. Meanwhile, the truck continued across the intersection and came to a stop on NE 140th Court, south of a retail business located on the intersection corner.

The driver and sole occupant of the car died in the crash; the commercial truck driver was not injured.

System performance data downloaded from the car indicated that the driver was operating it using the Traffic-Aware Cruise Control and Autosteer lane-keeping systems, which are automated vehicle control systems within Tesla’s Autopilot suite.

We became aware of the circumstances of the crash when the National Highway Traffic Safety Administration (NHTSA) began a defect investigation on June 28, 2016, which focused on the automatic emergency braking and Autopilot systems of the Tesla Models S and X, for model years 2014–2016. On learning of the May 7, 2016, Williston crash that prompted the NHTSA investigation, the NTSB initiated our investigation, which focused on the use of the Autopilot system.

We determined that the probable cause of the Williston, Florida, crash was the truck driver’s failure to yield the right of way to the car, combined with the car driver’s inattention due to overreliance on vehicle automation, which resulted in the car driver’s lack of reaction to the presence of the truck. Contributing to the car driver’s overreliance on the vehicle automation was its operational design, which permitted his prolonged disengagement from the driving task and his use of the automation in ways inconsistent with guidance and warnings from the manufacturer.

We made safety recommendations to the US Department of Transportation, NHTSA, manufacturers of vehicles equipped with Level 2 vehicle automation systems (Volkswagen Group of America, BMW of North America, Nissan Group of North America, Mercedes-Benz USA, Tesla Inc., and Volvo Car USA), the Alliance of Automobile Manufacturers, and the Association of Global Automakers. The NTSB also reiterates Safety Recommendations H-13-30 and -31 to NHTSA