And reportedly flagged the pedestrian as a 'false positive'

The self-driving Uber test vehicle which struck and killed a pedestrian in Tempe, Arizona reportedly didn't take evasive action because of problems with how the on-board software responds to foreign objects on the road.

A report in The Information quoting 'two people briefed about the matter' says the Volvo XC90 test car actually noticed Elaine Herzberg crossing the road, but didn't respond or take evasive action because the system designed to prevent false positives – to stop the car slamming on the brakes when a plastic bag floats across the road – was poorly tuned.

The threshold on the system was reportedly so low, it saw an adult woman and determined evasive action wasn't required.

Although the car was carrying a backup human driver, on-board video released by Tempe Police revealed he was distracted in the lead-up, repeatedly looking down. Warning: some viewers might find the footage distressing.

The vehicle was in autonomous mode when the collision occurred, with preliminary investigations suggesting the car was doing 40mph (around 60km/h) when it hit Herzberg. There were no significant signs of the vehicle slowing before the crash.

Things have unravelled quickly for Uber since the accident. Its self-driving test permit has been revoked in Arizona, while investigations into the company's test program have since revealed the number of human operators was cut, and the number of sensors on test cars reduced, in the months leading up to the crash.

Uber and the US National Transport Safety Board (NTSB) are both conducting investigations into the collision.

"We’re actively cooperating with the NTSB in their investigation. Out of respect for that process and the trust we’ve built with NTSB, we can’t comment on the specifics of the incident,” said an Uber spokesperson.

“In the meantime, we have initiated a top-to-bottom safety review of our self-driving vehicles programme, and we have brought on former NTSB chair Christopher Hart to advise us on our overall safety culture.

"Our review is looking at everything from the safety of our system to our training processes for vehicle operators, and we hope to have more to say soon.”