May 24 (UPI) -- An autonomous Uber vehicle that hit and killed an Arizona woman this spring detected her before the collision, but wasn't programmed to brake, federal investigators said Thursday.
The woman was killed near Phoenix on March 18 after she was hit by the self-driving vehicle while crossing the road.
In a preliminary report Thursday, the National Transportation Safety Board said the vehicle detected the woman 1.3 seconds before it hit her. It advised the human controller to stop but wasn't programmed to brake on its own, investigators said.
Uber said emergency braking is not enabled while its autonomous vehicles are under computer control. In other words, the human monitor sitting at the wheel is responsible for braking in that condition.
The NTSB, though, said the vehicle was not designed to warn the monitor of the impending collision. Investigators also said the female controller was "glancing down" at the time of the crash.
"The self-driving system data showed that the vehicle operator intervened less than a second before impact by engaging the steering wheel," the board said. "The operator began braking less than a second after the impact.
"The data also showed that all aspects of the self-driving system were operating normally at the time of the crash and that there were no faults or diagnostic messages."
The monitor said she was looking down to check the self-driving system interface, not a cellphone. In fact, she said, she didn't use any phone until she dialed 911 after the crash.
The NTSB report added the victim wasn't looking toward the oncoming vehicle until immediately before impact. She also wore dark clothing, rode a bicycle with no side reflectors and was crossing outside a crosswalk.
The woman's death was the first involving an autonomous vehicle in the United States.
Uber said Wednesday it halted self-driving vehicle tests in Arizona after the collision led the state to pull its permit. Consequently, Uber said it would lay off 300 workers in its Arizona division.