I think "zero" refers to the amount of enforcement SF is willing to commit to. I commute to SF daily; I can't remember the last time I saw someone being given a ticket for a moving violation. Maybe it happens in places I don't go, but I've literally not seen it occur in the last 20 years. (Parking tickets, sure, but that's about it.) Our politicians love to pass laws and feel proud of themselves for doing so. But from where I'm sitting, I see a lot of people not caring and doing whatever they want with zero consequences.