This is already happening. The first step is connected vehicles, which exist. Three transportation agencies have pilot projects for connected vehicles (http://www.its.dot.gov/pilots/). A car doesn't need to see a sign, but it will need pavement markings. Dow is already working on a marker that can go in paint, rather than an expensive transmitter under marking tape (like 3M will try to sell), that can be "seen" under snow.
The old saying in traffic engineering is that the you can't make the road totally safe because of the nut behind the wheel. Autonomous and connected vehicles remove that nut.