A truck driver's failure to yield the right of way and a Tesla driver's inattention due to over-reliance on automation were the principal causes that led to a fatal crash in Delray Beach, Florida, on March 1, 2019, according to a final report by the National Transportation Safety Board (NTSB).

The safety board said that the operational design of Tesla’s partial automation system contributed to the crash by permitting disengagement by the driver. The NTSB also cited Tesla's failure to limit the use of the system to design conditions and the failure of the National Highway Traffic Safety Administration to develop a method of verifying manufacturers’ incorporation of acceptable system safeguards for vehicles with Level 2 automation.

The accident vehicle. Source: NTSBThe collision involved a 2018 Tesla Model 3 car and a 2019 International semi-tractor trailer on U.S. Highway 441 in Delray Beach. The 50-year-old driver of the car died. The 45-year-old truck driver was uninjured.

“The Delray Beach investigation marks the third, fatal, vehicle crash we have investigated where a driver’s overreliance on Tesla’s “Autopilot” and the operational design of Tesla’s “Autopilot” have led to tragic consequences,” said NTSB chairman Robert Sumwalt.

The NTSB report said that the Tesla owner’s manual contains several warnings about Autosteer and the importance of a driver keeping his or her hands on the wheel.

The safety board said that based on system design, in an SAE-defined Level 2 partial automation system such as Autopilot, the driver holds responsibility to monitor the automation, maintain situational awareness of traffic conditions, understand the limitations of the automation and be available to intervene and take full control of the vehicle at any time. In practice, however, the NTSB said that it has found that drivers "are poor at monitoring automation and do not perform well on tasks requiring passive vigilance."

Still images from the Tesla's camera system showing the truck crossing the southbound traffic lanes seconds before the fatal collision. The NTSB said that the Tesla's collision avoidance system did not detect the truck in its path. Source: NTSBFollowing an earlier fatal crash that occurred in a scenario similar to the Delray Beach crash, the NTSB concluded that the way the Tesla Autopilot system monitored and responded to the driver’s interaction with the steering wheel "was not an effective method of ensuring driver engagement."

As a result, the NTSB recommended that Tesla and five other manufacturers of vehicles equipped with SAE Level 2 driving automation systems develop applications to more effectively sense the driver’s level of engagement and alert the driver when engagement is lacking while automated vehicle control systems are in use.

The NTSB said that the other five manufacturers responded to the NTSB's recommendation and described the actions they planned to take. "Tesla was the only manufacturer that did not officially respond to the NTSB about the recommendation," the Board said.

In late February, the NTSB said that multiple factors — including an ineffective driver monitoring system and driver distraction — led to a fatal March 2018 accident involving a Tesla vehicle on a highway in Mountain View, California.

The NTSB said that the driver in the Mountainview crash over-relied on the vehicle's “Autopilot” function and was likely distracted by a cell phone game app when the accident occurred. Even so, the NTSB faulted what it said was the Tesla vehicle’s "ineffective monitoring of driver engagement" as also contributing to the crash.

Delray Beach accident

The fatal March 2019 crash in Delray Beach, Florida, happened as the truck was crossing the southbound lanes of U.S. 441 to turn left into the northbound lanes. As the truck approached the intersection's stop sign, it slowed but did not come to a full stop before beginning to cross.

The car driver, traveling southbound at a recorded speed of 69 mph, did not apply the brakes or take any other evasive action to avoid the truck crossing in front of him. The Tesla hit the left side of the trailer just behind its midpoint. The car roof was sheared off as the car hit the trailer, traveled under it and continued south before coasting to a stop in the median about 1,680 ft from the point of impact.

Interior of a 2018 Tesla Model 3, similar to the vehicle involved in the fatal accident. Source: TeslaThe NTSB said that system performance data from the Tesla showed the driver was operating with the “Autopilot” engaged at the time of the collision. Data from the vehicle indicated the Tesla was traveling in the right lane of U.S. 441 when the driver activated the Traffic-Aware Cruise Control at a cruise speed of 69 mph, some 12.3 seconds before impact. The driver engaged “Autosteer” 2.4 seconds later, activating the “Autopilot” partial automation driving system.

The system did not detect steering wheel torque for the final 7.7 seconds before the collision, the NTSB said. The car’s forward collision warning and automatic emergency braking systems did not activate before the crash and there was no evidence of system- or driver-applied braking or steering before impact. NTSB investigators noted that the Delray Beach highway operating environment was clearly outside the “Autopilot” system’s operational design domain because the highway did not have limited access.

No hazard detected

The NTSB said that the Tesla's Autopilot system and collision avoidance systems did not identify the crossing truck as a hazard and did not attempt to slow the car. In addition, the driver did not receive a forward collision warning (FCW) alert, and the automatic emergency braking (AEB) system did not activate. Tesla told the NTSB that the installed FCW and AEB systems were not designed to activate for crossing traffic or to prevent crashes at high speeds.

The NTSB said the Tesla AEB system is a radar/camera fusion system designed for front-to-rear collision mitigation or avoidance. According to the company, the system requires agreement from both the radar and the camera to initiate AEB; complex or unusual vehicle shapes can delay or prevent the system from classifying the vehicles as targets or threats.

In this crash, according to Tesla, the Autopilot vision system did not consistently detect and track the truck as an object or threat as it crossed the path of the car. In addition, the NTSB said that "at no time" was there an object detection match between the car’s vision system and its radar data.