Tesla vehicles equipped with the Autopilot feature will not be recalled, federal safety regulators said today, after closing an investigation into a fatal crash.

The National Highway Traffic Safety Administration (NHTSA) closed its investigation into a Florida crash last May in which Joshua Brown was killed when his Model S crashed into the side of a semi-trailer that was crossing a highway. Investigators didn’t find a defect in Autopilot requiring a safety recall for Model S and Model X owners who have purchased that option.

“A safety-related defect trend has not been identified at this time and further examination of this issue does not appear to be warranted,” NHTSA said in a release.

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Tesla CEO Elon Musk praised the NHTSA report for being “very positive” in a Twitter message. In a second tweet, Musk cited the report crediting a nearly 40 percent drop in crash rate after Tesla began installing the Autosteer feature.

Autosteer, which can safely change lanes when the Tesla driver switches it on, was added to the Autopilot option in October 2015 with the Version 7.0 upgrade. In a tweet, Musk linked the Office of Defects Investigation’s report to NHTSA, which calculated crash rates by miles travelled prior to, and after, Autopilot installation and cited the 40 percent crash reduction.

Tesla Motors will need to wait until early summer for the second safety investigation to be reported on by the National Transportation Safety Board, an independent agency without regulatory power. NTSB usually conducts investigations into airplane crashes, but the Tesla Autopilot collision had garnered a great deal of concern over implications for the future of autonomous vehicle technologies.

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NHTSA acknowledged Tesla for adding protections to the Autopilot software that will prevent the use the system if drivers fail to pay attention. The agency found that Joshua Brown, a former Navy Seal and avid Tesla driver, made no attempt to brake, steer or take any other action to prevent the crash.

The Tesla system required “the continual and full attention of the driver to monitor the traffic environment and be prepared to take action to avoid crashes,” NHTSA said in the report.

The new safety feature was added in November as part of a new version of the Autopilot software. Another significant safety addition was emphasizing radar over cameras in the semi-autonomous guidance system. Musk said that the new safety feature could have helped Brown avoid the fatal crash.

Changes made to Autopilot system followed the company’s announcement of fully autonomous hardware being installed in all new Tesla vehicles manufactured starting in late October 2016. These new fully automated features will need government approval before being activated.

As for the Autopilot fatal crash, the case is closed.

“Tesla is not under any active investigation after today,” NHTSA spokesman Bryan Thomas told reporters.