The National Highway Traffic Safety Administration is upgrading its probe into 830,000 Tesla vehicles equipped with its Autopilot system, a key step for the agency to determine whether or not to order a safety recall, reports Reuters. A final decision could come within a year.

The 830,000 tally amounts to nearly all Tesla vehicles sold in the United States since the 2014 model year, according to the Associated Press.

Originally, NHTSA opened a preliminary evaluation to assess the advanced driver assistance system in 765,000 vehicles after 12 collisions in which Tesla vehicles hit immobile emergency vehicles. However, the auto safety regulators have expanded their investigation after recently identifying six additional crashes.

The upgraded probe is now classified as an engineering analysis. A key issue is whether or not some drivers think Autopilot is a self-driving feature that does not require their attention.

NHTSA said the upgrade is "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," notes the Reuters report.

NHTSA’s analysis determined Autopilot’s “Forward Collision Warnings (FCW) activated in the majority of incidents immediately prior to impact and that subsequent Automatic Emergency Braking (AEB) intervened in approximately half of the collisions.”

“On average in these crashes, Autopilot aborted vehicle control less than one second prior to the first impact,” the NHTSA notice said.

As reported by Reuters, NHTSA noted that "where incident video was available, the approach to the first responder scene would have been visible to the driver an average of 8 seconds leading up to impact."

The agency also reviewed 106 reported Autopilot crashes and said in approximately half, "indications existed that the driver was insufficiently responsive to the needs of the dynamic driving task.”