Tesla's Autopilot had no defects in it at the time of a fatal crash that spurred much criticism of the driver assistance system.
The National Highway Traffic Safety Administration closed its investigation of the system Thursday, and released its findings online.
"We learned a lot from this investigation," said NHTSA's communication director Bryan Thomas on a call with reporters Thursday afternoon, adding that the agency will continue to monitor the development of driver assistance and autonomous driving technology.
Thomas said Tesla was cooperative during the investigation, and that the ability to download data from cars to examine such events made the agency's investigation possible and that the ability to extract data like that "points to a bright future."
In addition to examining data, NHTSA took other measures, including surveying the crash site, and conducting road tests using a 2015 Tesla Model S 85D, which is similar to the car that crashed, and a 2015 Mercedes C300 4Matic, as a "peer vehicle."
In a statement, Tesla said, "the safety of our customers comes first, and we appreciate the thoroughness of NHTSA's report and its conclusion."
Tesla Chairman and CEO Elon Musk expressed satisfaction with the report's findings on Twitter.
But Thomas also said that drivers need to be fully aware and engaged, even when such driver assistance systems are operating, and that many crashes appeared to be influenced by driver behavior — in some cases cars appeared to be going too fast, drivers may have been distracted, or there may have been confusion over whether driver assistance systems were engaged. Some evidence from crash data suggests drivers may have engaged or disengaged the system without knowing prior to crashing.
"We are concerned about drivers operating these vehicles having good understanding of the capabilities and limitations of the systems in their vehicles," Thomas said, adding that owner manuals need to be clear about what these systems can and cannot do, and that some sort of driver training might be needed to educate drivers.
The announcement wraps up a roughly six-month investigation into whether a flaw in Tesla's Autopilot system led to the crash that killed a driver in Florida in May of 2016. NHTSA dispatched a team to inspect the site on June 21, and then opened its investigation a week later.
The NHTSA investigations are only intended to determine whether a safety defect led to a crash — beyond that the agency does not attempt to assess the root causes of a crash.