"The self-driving algorithms do not work because there has been some breakthrough in artificial intelligence; they run on maps. Every road that Google’s robo-cars drive on was first surveyed by a human-driven pilot car outfitted with sensors accurate enough to measure the thickness of the painted lines in the middle of the road. Every detail of the road has been mapped beforehand. According to Peter Norvig, Google’s head of research, it’s a hard problem for computer vision and artificial intelligence to pick a traffic light out of a scene and determine if it is red, yellow or green. But it is trivially easy to recognize the color of a traffic light that you already know is there."
http://www.nytimes.com/2013/12/15/magazine/googles-plan-for-...