A Tesla logo is seen at its planned store in Hanam Thomson Reuters WASHINGTON (Reuters) - The U.S. National Highway Traffic Safety Administration on Thursday is expected to close a six-month-old investigation into the death of a Tesla Motors Inc car driver using its semi-autonomous driving system Autopilot without seeking a recall, according to a source briefed on the matter.

The auto safety agency did not find evidence of a defect that would have required a safety recall of the cars, the source said.

Tesla in September unveiled improvements to its Autopilot software, adding new limits on hands-off driving and other improvements that chief executive Elon Musk has said likely would have prevented a fatality in May.

Tesla's Autopilot, introduced in October 2015, has been the focus of intense scrutiny since it was revealed in July that a Tesla Model S driver, Joshua Brown, was killed while using the technology in a May 7 collision with a truck in Florida.

(Reporting by David Shepardson)