First a little explanation of the image below.
This image is a graphical representation of the population of Manhattan during the day on the left and in the evening on the right. Notice the dramatic shifts indicating people work there but not many remain in the area after working hours. Further down are some stats from Frumination. Very interesting numbers done to research what it would take to replace the NYC Subway with vehicles.
The report also goes into how the NYC Subway is transporting 1,050 people into the CBD every 6 seconds!
The actual write up can be found here: http://frumin.net/ation/2009/08/whats_capacity_go_to_do_with_m.html
Here are the Frumination numbers: