[joosters]

I don't think it's the traffic law that is complex, but the liability involved. If my car picks its own speed and gets the speed limit wrong, who is responsible?

You could say that the ultimate responsiblity lies with the driver, but taking this position effectively means that all self-driving features are pointless (since this implies that the driver should be concentrating on the driving at all times).

If the responsibility lies (partially, at least) with the car manufacturer, they are going to get a lot of lawsuits thrown at them when it gets the speed limit wrong. Every speeding ticket, every accident where the car was going too fast, etc.