The desk where I work in San Francisco overlooks Cesar Chavez Street, a four-lane thoroughfare that starts at the eastern edge of the city, in the Bayview, and runs west at a jag for about three miles. Formerly known as Army Street, it is a largely charmless artery. In recent years, owing to procrastination, distraction, or general malaise, I've often found myself staring out at it, idly watching the traffic. There is nothing very unusual to see except for the Waymo cars--white, electric Jaguar S.U.V.s, kitted out with sensors and cameras, their rooftop LIDARs spinning. Self-driving cars are not a fixture of most American cities, at least not yet.