One of Uber’s testbed self-driving cars struck and killed a pedestrian early Monday morning in Tempe, Arizona, according to ABC 15. Tempe Police told ABC that the vehicle was in autonomous mode at the time, and that the woman was walking outside of the pedestrian crosswalk. If confirmed, that will make this the first time that someone has been killed by a fully autonomous vehicle.

According to ABC‘s reporting, the vehicle was driving itself at the time of the collision, but a driver was behind the wheel, as per the terms of Uber’s testing program. The company told The Verge that in response to the accident, it has pulled all its self-driving vehicles off the road in Arizona, as well as in other test locations in San Francisco, Toronto, and Pittsburgh.

“Our hearts go out to the victim’s family,” an Uber spokesperson told The Verge. “We are fully cooperating with local authorities in their investigation of this incident.”

Uber’s self-driving car trials have been running publicly since December 2016, when it first became possible for Uber users to hail a self-driving vehicle in San Francisco. Since then, Uber’s pilot program has expanded to Arizona, Pittsburgh, and Toronto. All of Uber’s self-driving vehicles are Volvo SUVs that have been modified with radar and LIDAR, as well as computer systems to process the data. Although Google’s Waymo self-driving cars have recently started going on public roads without a human physically inside, Uber’s vehicles still have a safety driver for now.

Tempe Police have not yet released any further details surrounding the collision, so there’s still a huge number of question marks surrounding the circumstances of the accident. If the collision was easily foreseen and avoidable, it will draw into question Uber’s safety protocols, as well as the effectiveness of Uber’s self-driving technology. If the pedestrian is found to be at fault, then it’s yet another tragic death attributable to motor vehicles.

While this is the first time a pedestrian has been hit and killed by a vehicle being driven autonomously, it’s not the first death attributable to a vehicle being driven by a computer. Tesla’s Autopilot, a semi-autonomous system that requires constant human supervision, has already been scrutinized in several fatal crashes.

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