The government has closed its investigation into a fatal crash between a Tesla on AutoPilot and a tractor-trailer that raised questions about the safety of autonomous vehicles, and the report offers a number of insights into the advanced driver assist technologies on the path to “self-driving” vehicles.

In May 2016, a Tesla Model S crashed into a tractor-trailer crossing an uncontrolled intersection on a Florida highway, killing the Tesla driver. The Tesla was being operated in Autopilot mode at the time of the collision, but the automatic emergency braking system did not provide any warning or automated braking. Nor did the driver take any braking, steering or other actions to avoid the collision.

The National Highway Traffic Safety Administration report determined that there was no safety-related defect involved in the crash. The agency noted that emergency braking systems like this are designed to reduce rear-end collisions, not crossing-path collisions like this one.

It also pointed out that Tesla’s Autopilot system “is an Advanced Driver Assistance System (ADAS) that requires the continual and full attention of the driver to monitor traffic and be prepared to take action to avoid crashes.”

But in this case, the driver did not have his hands on the wheel, and NHTSA said the crash appears to have involved a period of extended driver distraction (at least 7 seconds). The truck driver told a reporter that the driver of the Tesla was “playing Harry Potter on the TV screen” at the time of the crash.

Since the crash, Tesla has improved its system for monitoring driver engagement. If a driver doesn’t respond to visual cues in the driver monitoring system alerts, he or she may "strike out" and lose Autopilot function for the rest of the drive cycle.

While a report in Bloomberg said the system had been “vindicated,” the National Highway Traffic Safety Administration noted in its report that “the closing of this investigation does not constitute a finding by NHTSA that no safety-related defect exists. The agency will monitor the issue and reserves the right to take future action if warranted by the circumstances.”

However, NHTSA reported, an analysis of data supplied by Tesla indicated the Tesla vehicles crash rate dropped by almost 40% after Autosteer installation.

The agency analyzed mileage and airbag deployment data supplied by Tesla for all MY 2014 through 2016 Model S and 2016 Model X vehicles equipped with the Autopilot Technology Package, either installed in the vehicle when sold or through an OTA update, to calculate crash rates by miles travelled prior to and after Autopilot installation.