By which you mean they already exist today? My parents got a demo ride in one at a google event earlier this year. As long as the city involved is Mountain View, the vehicles already exist.
(Google's current effort relies on extremely detailed mapping of all the roads involved, but given the continued existence of the StreetView program that approach probably scales tolerably well.)
Mountain View doesn't really qualify as a "city" in the sense of city traffic. The roads are wide and not particularly densely packed. Not to downplay the accomplishment, but it's probably a long way from being able to handle San Francisco let alone New York or London.
(Google's current effort relies on extremely detailed mapping of all the roads involved, but given the continued existence of the StreetView program that approach probably scales tolerably well.)