A self-driving Uber car which struck and killed a pedestrian, detected the woman as she crossed the street, but chose not to react because of how its software had been reportedly tuned to avoid 'false positives.'

This is the understanding of Uber executives, according to two people who have been briefed on the matter ,and spoke anonymously to The Information.

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Uber and the US National Transportation Safety Board (NTSB) have been jointly investigating what caused the test vehicle to hit Elaine Hertzberg, 49, as she pushed her bicycle across a road in Tempe, Arizona on the night of March 18.

The Information claims the car's sensors detected Herzberg, but that its software decided not to react immediately. This, it is reported, was a result of how the software had been tuned to ignore false positives, like plastic bags floating out in front of the car. Unfortunately, one of the sources said Uber executives believe the software used in this incident had been tuned too far in that direction, causing the car to not react properly when seeing Hertzberg.

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The report claims that Uber's investigation found the car's sensors were likely working properly, combining data from cameras, lidar and radar systems to identify objects around it. The problem, the insiders claim, is what the car's broader system chose to do — or not do — with that information.

Meanwhile, footage released by Tempe Police shortly after the incident shows how the car's safety driver was looking down moments before the collision. According to an October 2017 video promoting its autonomous vehicles, Uber calls these employees "vehicle operators" and claims they are in the driver's seat "to make sure the vehicle does exactly what it's supposed to do."

Uber said in a statement: "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. In the meantimes, we have initiated a top-to-bottom safety review of our self-driving vehicles program, 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."

The incident raises serious concerns about the development of autonomous cars, and in particular the testing of these vehicles on public roads, as Waymo, General Motors, Toyota, Lyft and many other firms race to create fleets of robotic taxis without drivers.

Waymo, owned by Google parent Alphabet, announced in November 2017 that it soon plans to offer fully driverless rides to passengers in Arizona - that is, rides in a vehicle which has no safety driver behind the wheel. Meanwhile, only last week Lyft, a major rival to Uber, began operating an autonomous taxi service in Las Vegas, albeit one where a safety driver sits behind the wheel at all times.