The report said that the modified 2017 Volvo XC90 radar systems observed the pedestrian six seconds before impact but “the self-driving system software classified the pedestrian as an unknown object, as a vehicle, and then as a bicycle”.
At 1.3 seconds before impact, the self-driving system determined emergency braking was needed, but Uber said emergency braking manoeuvres were not enabled while the vehicle was under computer control in order to reduce the potential for erratic vehicle behaviour.
The Volvo XC90 is typically equipped with automatic emergency braking systems designed to prevent frontal crashes.
Uber Technologies Incorporated, which voluntarily suspended testing in the aftermath of the crash in the city of Tempe – the first death ever from a fully self-driving vehicle – said on Wednesday that it would shut down its Arizona self-driving testing programme and will focus on limited testing in Pittsburgh and two cities in California.
Arizona’s governor in March had suspended Uber’s permit for the testing, citing safety concerns.
The company did not directly comment on the NTSB findings but noted that it recently named a former NTSB chairman, Christopher Hart, to advise on Uber’s safety culture.
“As their investigation continues, we’ve initiated our own safety review of our self-driving vehicles programme,” the company said yesterday, adding that it planned to announce changes in the coming weeks.
All aspects of the self-driving system were operating normally at the time of the crash, and there were no faults or diagnostic messages, the NTSB said.
The report gives new fuel to opponents in Congress who have stalled a bill designed to speed the deployment of self-driving cars onto US roads and puts a spotlight on the fact that the National Highway Traffic Safety Administration, which is also investigating, does not test self-driving vehicles or certify them before they are deployed on US roads.
Uber aims to resume self-driving operations this summer, likely with smaller routes and fewer cars, the company said on Wednesday.
Elaine Herzberg, 49, was walking her bicycle outside the crosswalk on a four-lane road when she was struck by the Uber vehicle travelling at about 40mph (64kph).
A safety operator behind the wheel appeared to be looking down, and not at the road, moments before the crash, according to video from inside the car released by police.
The operator told the NTSB that she was not looking at a mobile phone but monitoring the vehicle’s self-driving systems.
Tempe police said on Wednesday they had completed their investigation and turned the findings over the prosecutors to review.
Police did not release the results of the probe.
The NTSB said that the Uber vehicle required the operator to intervene and take action, but the system is not designed to alert the operator.
The report said the operator engaged the steering wheel less than a second before impact and began braking less than a second after impact.
The report noted that Herzberg tested positive for methamphetamine and marijuana, and that she did not look in the direction of the vehicle until just before impact.
The NTSB did not say when it would release its final report on the accident.
The agency typically issues its final conclusions at least a year after an accident.