Pilot models of the Uber self-driving car is displayed at the Uber Advanced Technologies Center on Sept. 13, 2016.

On Sunday night, an autonomous car operated by Uber — and with an emergency backup driver behind the wheel — struck and killed a woman on a street in Tempe, Ariz. It was believed to be the first pedestrian death associated with self-driving technology. The company quickly suspended testing in Tempe as well as in Pittsburgh, San Francisco and Toronto.

The Uber car, a Volvo XC90 sport utility vehicle outfitted with the company’s sensing system, was in autonomous mode with a human safety driver at the wheel but carrying no passengers when it struck Elaine Herzberg, a 49-year-old woman, on Sunday around 10 p.m.

A self-driving Uber car at the scene of a fatal accident in Tempe, Arizona

Sgt. Ronald Elcock, a Tempe police spokesman, said during a news conference that a preliminary investigation showed that the vehicle was moving around 40 miles per hour when it struck Ms. Herzberg, who was walking with her bicycle on the street. He said it did not appear as though the car had slowed down before impact and that the Uber safety driver had shown no signs of impairment. The weather was clear and dry.

Waymo, which has been testing autonomous vehicles on public roads since 2009 when it was Google’s self-driving car project, has said its cars have driven more than 5 million miles while Uber’s cars have covered 3 million miles.

In 2016, a man driving his Tesla using Autopilot, the car company’s self-driving feature, died on a state highway in Florida when his car crashed into a tractor-trailer that was crossing the road. Federal regulators later ruled there were no defects in the system to cause the accident.