Understanding Tesla Autopilot Accident


As National Highway Traffic Safety Administration (NHTSA) continues its investigation, let’s try to “understand” what happened. But before getting into that, lets see how Tesla’s autopilot system works. As i was told, the autopilot system is a continuously learning AI. It learns from its drivers everytime they drive the car on auto pilot. As it learns that way, it also teaches all Teslas over a network. So if you own one, your car too is a part of that fleet.

So how exactly does this work? According to Elon, there are 4 pillars for autonomous driving. A Long Distance Radar, Cameras, Ultra Sonic Sensors and Satellite imagery with real time traffic data. All these 4 are integrated together to make the autopilot system work.


With regards to this particular accident, which is said to be the first known fatality involving an autonomous driving car, folks at Electrek have come-up with a sketch based on police inputs, and as the visualization shows, the car passes underneath the trailer tearing its roof apart, continuing on the road for few hundred feet and hits couple of fences before finally coming to rest.

“When the truck made a left turn onto NE 140th Court in front of the car, the car’s roof struck the underside of the trailer as it passed under the trailer. The car continued to travel east on U.S. 27A until it left the roadway on the south shoulder and struck a fence. The car smashed through two fences and struck a power pole. The car rotated counter-clockwise while sliding to its final resting place about 100 feet south of the highway.” – The Florida Highway Patrol

Tesla had this to say in its blog – “What we know is 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 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.”

This statement raises an obvious concern. The autopilot system uses camera’s contrast detection alone? What happened to the on-board radars? For those who had this question, Musk had an explanation – 

So as it turns out, the radar systems misjudged the height. The Tesla blog also adds that when drivers activate Autopilot, the acknowledgment box explains, among other things, that Autopilot “is an assist feature that requires you to keep your hands on the steering wheel at all times,” and that “you need to maintain control and responsibility for your vehicle” while using it. Additionally, every time that Autopilot is engaged, the car reminds the driver to “Always keep your hands on the wheel. Be prepared to take over at any time.” The system also makes frequent checks to ensure that the driver’s hands remain on the wheel and provides visual and audible alerts if hands-on is not detected. It then gradually slows down the car until hands-on is detected again.

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