Spotted one of these near me on the overpass today. I had no idea what it was. A cylinder about the size of a paint can was mounted on top, and spinning like hell. Then I saw the sticker on the back: “Google self-driving car.”
Looked it up later. That thing is a laser rangefinder that creates a 3D image of its surroundings, combined with other sensors. In the city, I assume a driver is inside at all times, just in case. At least someone was sitting in the drivers seat of this one.