Elaine Herzberg was crossing a street late during the night of March 18 in Tempe, Arizona, when she was killed by an Uber self-driving car, calling autonomous vehicles into question.

“Testing must occur safely,” Tempe Mayor Mark Mitchell said. “All indications we have had in the past show that traffic laws are being obeyed by the companies testing here. Our city leadership and Tempe police will pursue any and all answers to what happened in order to ensure safety moving forward.”

These cars are operated with a driver in the driver’s seat, but has an autonomous mode where the driver is just monitoring in case something were to happen. The car that hit Herzberg was on this autonomous mode.

The woman was said to have come out of the shadows, making it so the camera on the car couldn’t detect her. However, the driver behind the wheel was distracted at the time and wasn’t paying attention. If he had, investigators say he possibly could have stopped the accident from happening.

Uber’s self-driving cars started in Arizona because of little inclement weather. These cars can struggle in rain or snow, so Arizona has become a breeding ground for this new technology. The company started with self-driving trucks, which usually drive on highways where the less complicated setting cooperates with the technology. Now, there are cars being tested on the roads in about 30 cities around the country.

After the accident, Uber temporarily stopped car tests in Arizona, Toronto, San Francisco and Pittsburg. They also apologized to Herzberg’s family.

“As we develop self-driving technology, safety is our primary concern every step of the way,” Uber spokesman Matt Kallman said. “We’re heartbroken by what happened this week, and our cars remain grounded. We continue to assist investigators in any way we can.”

Several other companies besides Uber are testing their own self-driving cars. One of these companies is Waymo who, as reported by The New York Times, has far exceeded Uber. While Uber’s cars can go 13 miles without human intervention, Waymo’s cars can go 5,600 miles without a driver stepping in to help. Waymo CEO John Krafcik was featured in a recent Forbes article.

“What happened in Arizona obviously was a tragedy,” John Krafcik said. “We’re very confident that our car could have handled that situation.”

The accident is under investigation now. Uber will keep improving its technology, in order to prevent another accident like this from happening.