While responding to reports of what looked like a routine car crash early on the evening of March 24, Officer Dustin Patterson of the Tempe, Arizona, police department became an unwitting pioneer of the autonomous age.
On arriving at the scene, Patterson learned that one of Uber?s self-driving cars was among the four vehicles involved. The company had started testing in this Phoenix suburb only three months earlier; this marked the first time one of the city?s police officers would investigate a crash that involved a car traveling in autonomous mode.
Within minutes, Patterson determined the Uber car was not at fault. A human driver had made a normal human mistake, turning left at an intersection into the path of the Uber car, which was a 2017 Volvo XC90 SUV. It was a simple case of failure to yield. Determining how to handle a crash involving an autonomous vehicle, however, was more complex. For starters, the official Arizona crash-report document used to collect information on collisions contains spaces for hundreds of variables?ranging from weather at the time of the crash to whether wild animals or livestock were contributing factors. But none of the spaces allow officers to denote that a car was operating under control of a self-driving system.

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?The disturbing thing for me is that they?ve been, by and large, left out of the discussion so far.? ? Jim Hedlund, Governors Highway Safety Association

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This was a minor crash, and all vehicle occupants walked away. Had...