Vox describes the detailed mapping Google and others will have to do to support their autonomous cars. And Brad Plumer describes five challenges: mapping; social interactions between car and other people; bad weather; regulations; cybersecurity.
These innovations seem to be coming from different directions: cars which drive themselves on preregistered courses (there was a piece on an outfit in the Netherlands which produces upscale gold carts for such applications); cars with improvements, like today's safety stuff; cars which are as independent of outside help as the old model of human driving car (the Tesla model). It's partly the old question, which is better distributed intelligence or central guidance. We shall see.