I have a daughter who lives in the City and she said most everybody knew about it a couple of days ago. She didn’t think many were going to participate but she knew about it
I'm not quite there, though I'm not all that far away. (You don't have to tell us, but I wonder where she is. Maybe awareness was greater in certain neighborhoods that got leafletted or something.)
If there was any attempt at spreading an announcement to the wider world, someone didn't do it very well. According to online traffic maps and other reports, there was a backup that lasted for some time. (Besides, if you wished to obstruct traffic, thereby somehow antagonizing people into agreeing with your views, you'd want someone to obstruct.)