My apartment overlooks Broadway, a few blocks south of 14th Street in Manhattan. Cars and trucks go by pretty much 24 hours a day; Broadway is the most direct route downtown, and every trucker knows it. Even on the 10th floor where I live, the drone is steady and persistent. I have always found the sound comforting in a way, as if it's direct proof that life and activity and commerce continue even as I sleep.
The only time the traffic stops moving on Broadway is when we get a lot of snow. A big snowfall takes a day or two to be cleared away, and for awhile, there's an eerie silence, as if all the normal activity of the city has been muffled and deadened.
That's what it was like in the several days following 9/11. Traffic was closed off below 14th Street. Only black cars with tinted windshields and government license plates occasionally roamed the streets. That eerie dead quiet is what I remember most of all. It was so quiet it was hard to think, it was hard to sleep, it was hard to do much of anything.