I was taking a nap before attending the next day of the New York Salsa Congress and was woken up by screaming sirens of what seemed to be hundreds of emergency vehicles. Also I heard some strange roaring sound. I thought another terrorist attack happened and half-a-sleep I looked outside the window to see what was happening. I saw a bunch of motocycles zooming through the interecection outside of my apartment building. They were coming and coming and coming... This continued for something like 10-15 minutes!
As I looked to the left along 8th avenue, I saw the gridlock for several blocks. The pissed of drivers were honking to relieve their stress as they were waiting for the traffic directors to allow them to go through the green light. After watching the news I found out that this was a procession of more than 1,2000 motorcycles to honor the victims of the World Trade Center Attack. Here is the official press release from Port Authority of New York and New Jersey.

Later on my way to the Salsa Congress, I saw a bunch of those motorcycles parked on 53rd street.