The Tesla driver killed in a crash while the Autopilot system was activated last year would have seen the tractor trailer for at least seven seconds prior to impact, according to the NHTSA investigation of the accident. This should have given the driver enough time to take “some action,” said Bryan Thomas, communications director for NHTSA, though it’s not known “whether that was enough time to avoid or mitigate the crash.”

The NHTSA investigation report called seven seconds a “period of extended distraction,” and noted that similar crashes generally had a “much shorter time” available for both the system and driver to detect and respond to a pending collision, usually less than three seconds. The report called distractions longer than seven seconds to be “uncommon, but foreseeable.”

There is no word from NHTSA about what the driver was doing during those seven seconds, though the driver of the tractor trailer truck involved in the accident claimed the Tesla driver was watching a Harry Potter movie. His last interaction with the car was to set the cruise control speed to 74 mph less than two minutes before the crash.

From the NHTSA report:

An attentive driver has superior situational awareness in most of these types of events, particularly when coupled with the ability of an experienced driver to anticipate the actions of other drivers. Tesla has changed its driver monitoring strategy to promote driver attention to the driving environment.

Every time Autopilot is activated, the system advises drivers to keep their hands on the wheel and “be prepared to take over at any time.” Regardless of the potential for distraction, the report also found that crash rates for Tesla vehicles dropped by 40 percent after Autopilot was installed.

The report notes that Automatic Emergency Braking (AEB) systems, like those installed in the Tesla at the time of the crash, are not designed to avoid “left turn across path” collisions. Instead, the system is designed primarily to avoid rear-end collisions. The AEB in this generation of Tesla’s vehicles “requires agreement” between the camera and radar systems before initiating automatic braking.

Autopilot requires the “continual and full attention” of the driver

The NHTSA report concludes that Autopilot requires the “continual and full attention” of the driver, and that they should be prepared to “take action to avoid crashes.” Autopilot is an “assistance system” and is not meant, nor is it capable, of taking full control of driving functions over from the driver.

NHTSA also notes that Tesla has provided extensive information about the system’s limitations to owners and encouraged drivers to remain engaged in the driving task at all times. NHTSA found no defects in design or performance of Autopilot.

“At Tesla, the safety of our customers comes first, and we appreciate the thoroughness of NHTSA’s report and its conclusion,” said a Tesla spokesperson to The Verge.