Earlier quoted context omitted.
> the illegality of the U turn is implicit, the software learned that the path was valid from other drivers One would hope that the traffic laws of an area are "hard coded" and not dependent on what other drivers do.
I don’t think you can really bake that in because the traffic rules can change day-to-day. For example, there’s a street in my neighborhood that’s normally open for two-way traffic, but one of the buildings that fronts it is being renovated so the street was changed to one-way for about a month, and as of a couple of days ago it’s still one-way but in the other direction. Imagine trying to get a car to work that out…
The point I was making is that these cars should absolutely not be "learning" what rules to follow by observing what other drivers actually do. When there is no clear signage, there are well-defined laws about what drivers need to do and self-driving cars need to follow those even if human drivers don't.