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The National Highway Traffic Safety Administration (NHTSA) has deepened (PDF) its investigation into a series of Tesla crashes involving first responders to an engineering analysis. As The Washington Post explains, that’s the last stage of an investigation, and the agency typically decides within a year if a vehicle should be recalled or if the probe should be closed. In addition to upgrading the probe’s status, the investigation now covers 830,000 units, or almost all the Tesla Model Y, Model X, Model S and Model 3 vehicles the company has sold since 2014.

This development expands upon the investigation the NHTSA initiated back in 2021 following 11 collisions of Tesla vehicles with parked emergency responders and trucks. Since then, the agency has identified and added six more incidents that occurred over the past couple of years. In most of those crashes, Autopilot gave up vehicle control less than one second before impact, though Automatic Emergency Braking intervened in at least half of them. 

The NHTSA also found that the first responders on the road would’ve been visible to the drivers at an average of eight seconds before impact. Plus, forensic data showed no driver took evasive action between 2 to 5 seconds prior to impact even though they all had their hands on the wheel. Apparently, nine of the 11 vehicles originally involved in the investigation exhibited no driver engagement visual or chime alerts until the last minute before the collision. Four of them didn’t exhibit any engagement visual or chime alert at all. 

The NHTSA also looked into 191 crashes not limited to incidents involving first responders. In 53 of those collisions, the agency found that the driver was “insufficiently responsive” as evidenced by them not intervening when needed. All these suggest that while drivers are complying with Tesla’s instructions to make sure they have their hands on the wheel at all times, they’re not necessarily paying attention to their environment. 

That said, the NHTSA noted in its report that “a driver’s use or misuse of vehicle components, or operation of a vehicle in an unintended manner does not necessarily preclude a system defect.” As University of South Carolina law professor Bryant Walker Smith told The Post, monitoring the position of a driver’s hands isn’t effective enough, because it doesn’t ensure a driver’s capability to respond to what they encounter on the road. 

In addition, the NHTSA noted that the ways a driver may interact with the system is an important design consideration for Level 2 autonomous driving technologies. These systems still aren’t full autonomous and still mostly depend on the human driver, after all. “As such, ensuring the system facilitates the driver’s effective performance of this supervisory driving task presents an important safety consideration,” the agency wrote.