The National Highway Traffic Safety Administration is about to take a closer look at Tesla's Autopilot, the company revealed on Thursday. In a blog post, Tesla says that it learned on Wednesday evening that the NHTSA is "opening a preliminary evaluation into the performance of Autopilot" following a fatal crash involving a Model S.

The incident, which happened in May, involved a white tractor-trailer that was turning left across a divided highway, perpendicular to the path of the Tesla, which was cruising on Autopilot. "Neither Autopilot nor the driver noticed the white side of the tractor trailer against a brightly lit sky, so the brake was not applied. 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 impacting the windshield of the Model S," Tesla stated.

The company also stated that in a front-on or rear-end collision with the tractor-trailer, the outcome would not have ended in tragedy. It described the driver as "a friend to Tesla and the broader EV community" and expressed sympathy for his friends and family for their loss.

Although Tesla's Autopilot is one of the very best semi-autonomous driving systems on the market, it is not designed for "eyes-off" driving, and owners should be as vigilant on the roads as they would be in any other vehicle.

[Originally we wrote that the tractor-trailer crossed the highway divider, giving the impression it was out of control; this has been corrected.]