When Ken Rosenberg thinks about self-driving cars, a particular incident comes to mind.
"One of the autonomous vehicles stopped in the middle of the road. There was a chicken running around the street, and the car didn't know what to do. But it wasn't just the chicken, a woman in a wheelchair was chasing the chicken. The car just basically shut down."
Rosenberg is vice mayor of Mountain View, California, where Google is headquartered. He was in the audience at the annual City Summit of the National League of Cities, held this year in Pittsburgh.