The fire truck had its emergency lights flashing while responding to an earlier crash and was parked across a left-hand lane on Interstate 70 roughly 72km west of Indianapolis when it was hit by the Tesla, the Indiana State Police said in a Dec 29 statement.

The 23-year-old wife of the Tesla’s driver died of her injuries at a hospital, according to the statement.

The 25-year-old driver was injured. No firefighters were hurt.

The state police said they planned to reconstruct the crash, which occurred about 8am, as part of their investigation, and that drugs and alcohol were not contributing factors.

NHTSA did not specify whether Tesla’s collection of automated driver-assist technologies known as Autopilot were active in the Indiana crash, but the investigation follows a series of inquiries opened into such crashes.

NHTSA has looked into 23 crashes in which some form of automated driver-assist technologies were believed to be in use at the time of the collisions.

Of those, 14 of involved Tesla models, NHTSA said in its statement.