The New York City subway system is the oldest underground public transportation network in the US, and one of the largest in the world. It consists of some 468 stations, and more than 1000 km of tracks. Actually, about 40% of the ’subway’ runs above the ground, but its tracks are completely separated from road traffic. The first underground subway line was opened in 1904. The various privately owned lines and companies were purchased by the City of New York and united under the New York City Transit Authority in 1953, renamed Metropolitan Transportation Authority (MTA) in 1968. During weekdays, about 4.5 million passengers use the subway every day. The famous tokens (metal pieces similar to coins) which were used for decades to enter a subway station were phased out in 2003, replaced by magnetic MetroCards, which can store the amount of money ’put on it’ by the passenger, as well as adding to or subtracting from it.