Uber will not face criminal charges for a fatal crash involving one of its self-driving cars.

Prosecutors have ruled that the company is not criminally liable for the death of Elaine Herzberg, 49, who was struck as she crossed a road in Tempe, Arizona.

The car's back-up driver could still face criminal charges.

"After a very thorough review of all evidence presented, this office has determined that there is no basis for criminal liability for the Uber corporation," wrote Yavapai County Attorney Sheila Sullivan Polk in a letter.

The crash occurred in March 2018, and involved a Volvo XC90 that Uber had been using to test its self-driving technology.

Just before the crash, Ms Herzberg had been walking with a bicycle across a poorly lit stretch of a multi-lane road.

Dash-cam footage released by police after the incident appeared to show the vehicle's back-up driver, Rafaela Vasquez, taking her eyes off the road moments before the crash.

Further records from the streaming service Hulu suggested that Ms Vasquez had been streaming a TV show on a phone at the time of the crash.

Uber did not respond to a request for comment.

The National Transportation Safety Board is also investigating the crash. It released a preliminary report last year that suggested the sensors on the Uber vehicle were working correctly, but that emergency braking manoeuvres may not have been enabled.

Following the crash, authorities in Arizona suspended Uber's ability to test self-driving cars on the state's public roads.

In December, Uber resumed limited self-driving car testing in Pittsburgh, restricting the cars to a small loop they can drive only in good weather. The company is now testing with two people in the front seat and more strictly monitors safety drivers. The company also said last year it made improvements to the vehicles’ self-driving software.