— -- Federal investigators announced Tuesday that the design of Tesla's semiautonomous driving system allowed the driver of a Tesla Model S in a fatal 2016 crash with a semi-truck to rely too heavily on the car's automation.
"Tesla allowed the driver to use the system outside of the environment for which it was designed," said National Transportation Safety Board Chairman Robert Sumwalt. "The system gave far too much leeway to the driver to divert his attention."
The board's report declares the primary probable cause of the collision as the truck driver's failure to yield, as well as the Tesla driver's overreliance on his car's automation — or Autopilot, as Tesla calls the system. Tesla's system design was declared a contributing factor.
In May 2016, Joshua Brown was driving his Tesla on a Florida highway when the vehicle collided with the side of a truck making a left turn from an oncoming lane. Investigators said they do not know if the truck driver saw the approaching car, because the driver refused requests to be interviewed. Brown was killed in the crash.
An NTSB analysis of a toxicology test found the truck driver used marijuana before the crash, but NTSB investigators could not conclude his level of impairment, if any.
The NTSB said Green's vehicle performed as designed but could be improved to deter drivers from diverting their attention from the road.
"While automation in highway transportation has the potential to save tens of thousands of lives, until that potential is fully realized, people still need to safely drive their vehicles," Sumwalt said.
Tesla made updates to its Autopilot design after the crash, warning drivers earlier after they remove their hands from the steering wheel.
A Tesla spokesperson provided a statement to ABC News that read, "We appreciate the NTSB's analysis of last year's tragic accident, and we will evaluate their recommendations as we continue to evolve our technology. We will also continue to be extremely clear with current and potential customers that Autopilot is not a fully self-driving technology and drivers need to remain attentive at all times."
According to The Associated Press, members of Brown's family said on Monday that they do not blame the car or the Autopilot system for his death.