The nation's top auto safety regulator, the National Highway Traffic Safety Administration, said late Wednesday that it had begun an investigation of a second crash involving a Tesla Motors car equipped with autopilot technology, a system designed to let vehicles drive themselves for brief periods.
In the nonfatal crash, a Tesla Model X SUV that the driver said was on autopilot rolled over last Friday on the Pennsylvania Turnpike after hitting barriers on both sides of the highway.
Meanwhile, safety officials continue to investigate a fatal Williston accident in May, the first known fatality involving an autonomous driving system, in which the driver was killed when his Tesla Model S sedan struck a semitrailer truck that was crossing the road.
The accidents shine new scrutiny on Tesla's autopilot system and raised questions about whether the technology, which the company describes as only an experimental "beta" test, lulls drivers into a false sense of security.
An account given Wednesday by a witness to the Williston accident seemed to indicate the autopilot system continued operating the car at highway speed, even after its top was sheared off by the impact and the Tesla went under the semi and continued down the road.
"The top was gone. It went right by me," said Terence Mulligan, who was driving behind the semi at the time.
In a statement about the Pennsylvania crash, Tesla said it had "no reason to believe that autopilot had anything to do with this accident" based on the information it had collected so far.
Tesla vehicles have the ability to send data to the company about their condition and operation. In a statement, the company said it received an automated alert from the Model X in Pennsylvania on July 1 showing that its airbags had deployed. But it said more detailed information about the car's operation was not received, a situation that could happen if the car's antenna was damaged in the crash.