The NTSB determined that Joshua Brown's Model S was traveling at 74 mph in Autopilot mode when it struck a truck. Photo credit: NTSB

The Tesla Model S that crashed into a semi-truck while operating in Autopilot mode was driving over the posted speed limit for the road, according to a newly released report from the National Transportation Safety Board.

The agency said Joshua Brown’s Model S was traveling 74 mph with the Autopilot engaged when he collided with the truck, which was in the middle of turning on to the roadway. The speed limit for the road was 65 mph.

“Tesla system performance data downloaded from the car indicated that vehicle speed just prior to impact was 74 mph,” the NTSB said in a preliminary report on its investigation of the crash.

“System performance data also revealed that the driver was operating the car using the advanced driver assistance features Traffic-Aware Cruise Control and Autosteer lane keeping assistance.”

Brown, who was described as a Tesla disciple, reportedly bragged earlier about how the Autopilot avoided a crash. However, this time there was a mitigating factor.

“Neither Autopilot nor the driver noticed the white side of the tractor-trailer against a brightly lit sky, so the brake was not applied,” Tesla said in a blog post.

Tesla CEO Elon Musk said that splitting with Autopilot supplier Mobileye was "somewhat inevitable."

(Tesla plans to improve Autopilot, Musk says. Click Here for more.)

In the wake of the fatal accident, the California-based EV maker is parting ways with Mobileye, the Israeli manufacturer of the sensors used as part of the Autopilot system. Tesla CEO Elon Musk discussed the split while on a tour of the company’s new Gigafactory in Nevada.

“Us parting ways was somewhat inevitable. There’s nothing unexpected here from our standpoint,” Musk said, according to USA Today. “We’re committed to autonomy. They’ll go their way and we’ll go ours.”

The company will continue to support current Tesla products, including upgrades to the Autopilot system, said Chairman Amnon Shashua during the company’s second-quarter earnings release earlier this week. The improvements should help with crash avoidance and better allow the car steer itself.

However, Mobileye’s system is not designed to detect cross traffic yet, the company said in a statement after the incident. It’s supposed to work in concert with other systems to handle this sort of situation. Tesla said Autopilot, which combines proprietary and third-party technology, is designed to recognize “interruption of the ground plane” in front of the vehicle.”

(Automakers can’t sacrifice safety in rush to autonomous driving. For more, Click Here.)

However, the high, white side of the trailer attached to the truck, combined with a radar signature that would have been interpreted as an overhead sign. The braking system did not activate as a result. The Model S struck the 53-foot-long truck and passed under it, killing Brown in the process. He was pronounced dead at the scene.

“As a result of the initial impact, the battery disengaged from the electric motors powering the car,” the agency said. “After exiting from underneath the semitrailer, the car coasted at a shallow angle off the right side of the roadway, traveled approximately 297 feet, and then collided with a utility pole.”

The NTSB used three-dimensional laser scanning technology to document “the crash location, the damaged semitrailer and the damaged car.” The investigation also utilized data obtained from Tesla’s on-board computer systems, which can record and transmit vehicle performance data. The National Highway Traffic Safety Administration is also conducting an investigation.

(Consumer Reports wants Autopilot shut off. Click Here for that story.)

The investigation is not complete, the report focuses on the initial findings by investigators. The NTSB “will continue to collect and analyze these data, and use it along with other information collected during the investigation in evaluating the crash events.”

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