The preliminary report, issued by the National Transportation Safety Board, said on Thursday that while the vehicle’s guidance system had spotted the woman about six seconds before hitting her, emergency braking manoeuvres were not enabled in order to “reduce the potential for erratic vehicle behavior”.
Instead, the Uber system anticipated that the human back-up driver would intervene. However, the automated system was not designed to alert the driver of the impending danger.
The car was traveling at 43 miles per hour and its sensors determined that braking was needed 1.3 seconds before impact, according to the report.
But the driver began to steer less than a second before striking 49-year-old Elaine Herzberg, who was pushing a bicycle across a boulevard in the darkness in Tempe, Arizona, when the crash took place. The vehicle’s brakes were not applied until after the fatal impact.
In an interview with NTSB investigators, Uber’s back-up driver said she had been monitoring the “self-driving interface”.
On Wednesday, Uber announced it would cease testing its vehicles in Arizona and would focus on more limited testing in Pittsburgh, Pennsylvania, and California.
Uber said that it had worked closely with the NTSB and was conducting an internal review of its self-driving vehicle program.
The company also announced it had brought in the former NTSB chairman Christopher Hart “to advise us on our overall safety culture, and we look forward to sharing more on the changes we’ll make in the coming weeks”.
The NTSB said its preliminary report was not designed to assign responsibility for the crash.