Here's 24 hours' worth of (pre-hurricane) transit in New York City compressed into a little over two minutes. There's a date/time stamp at upper right. Even in New York there's markedly less activity in the wee hours of the morning, but it never stops entirely. It's sort of like watching the human equivalent of an ant farm, but when you think about all the people those trains and buses are carrying it's striking.
Click through to YouTube for more details.
And while we're talking transit, here's something else interesting, a collection of subway-style maps used to convey other information, from layout of the U.S. highway system (which isn't all that conceptually removed) to popular film genres rendered as subway lines and well-known films as stations on the lines, and sometimes on more than one of them:
I should credit Moshe Feder for putting me onto both these items.