Tesla said that the vehicle was on a divided highway with autopilot engaged when a tractor trailer drove across the highway perpendicular to the Model S. “Neither Autopilot nor the driver noticed the white side of the tractor trailer against a brightly lit sky, so the brake wasn’t applied,” Tesla said. 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 hitting the windshield of the Model S.

http://www.theaustralian.com.au/business/us-driver-killed-while-tesla-electric-car-on-autopilot-mode/news-story/4054800cb8e2b2975ccfa04e92bfc744