In recent years Tesla electric vehicles running Autopilot technology have been involved in high-profile crashes, prompting regulators in the United States to probe the cause of the accidents, some of which have proved fatal.

One of the organisations involved in investigating Tesla is the National Highway Traffic Safety Administration (NHTSA), which has this week confirmed an intensifying (PDF) of its probing.

“PE21-020 (Preliminary Evaluation) is upgraded to an Engineering Analysis (EA) to extend the existing crash analysis, evaluate additional data sets, perform vehicle evaluations, and to explore the degree to which Autopilot and associated Tesla systems may exacerbate human factors or behavioral safety risks by undermining the effectiveness of the driver’s supervision,” the NHTSA explains.

“In doing so, NHTSA plans to continue its assessment of vehicle control authority, driver engagement technologies, and related human factors considerations,” it adds.

As Engadget points out, this means that as many as 830 000 Tesla vehicles could be recalled should the Autopilot technology be deemed an unsafe driving aid, effecting nearly the entire fleet of commercial EVs that the company has sold since 2014.

The Washington Post, which initially covered the development, has pushed Tesla for comment on the matter, but is yet to receive a response at the time of writing.

“NHTSA reported that it has found 16 crashes into emergency vehicles and trucks with warning signs, causing 15 injuries and one death,” noted the publication from the NHTSA report.

“In the majority of the 16 crashes, the Teslas issued collision alerts to the drivers just before impact. Automatic emergency braking intervened to at least slow the cars in about half the cases. On average, Autopilot gave up control of the Teslas less than a second before the crash, NHTSA said in documents detailing the probe,” it added.

The NHTSA also looked into an estimated 191 crashes, outside of the first responder ones, with 53 of the collisions finding that the driver of the Tesla vehicle was “insufficiently responsive”.

“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,” the NHTSA report pointed out.

With Tesla EVs not being fully autonomous, the way the driver interacts with the system is important. “As such, ensuring the system facilitates the driver’s effective performance of this supervisory driving task presents an important safety consideration,” the agency concluded.

There is no mention of when the intensified investigation will be completed, but a less than favourable outcome for Tesla could scupper any future Autopilot plans, not to mention the cost that a massive recall would entail.