What is the busiest Metro (subway) line in the world?

Question

What is the busiest metro (underground or subway) line in the world? How many passengers per hour at peak times? How many passengers can each carrage fit, and how many for each train?

Answer 1

Shinjuku Station (新宿駅, Shinjuku-eki?) is a train station located in Shinjuku and Shibuya wards in Tokyo, Japan.

Serving as the main connecting hub for rail traffic between central Tokyo and its western suburbs on inter-city rail, commuter rail and metro lines, the station was used by an average of 3.31 million people per day in 2006, making it the busiest train station in the world in terms of number of passengers. (For the exact number, see the discussion below.) Including an underground arcade, there are well over 200 exits.