Another good question is what does the car do if the stop sign or traffic light is obscured by trees?

I swear to good the city of San Francisco could car less about this issue. I've gotten to the point where I look for the painted STOP on the road, rather than the stop sign.

I assume either the computer could recognize the painted letters on the road (they are often in bad shape) or the GPS would inform the computer that a stop sign exists? So it doesn't have to look for it?