most extensive metro systems in the world

This combined urban rapid transit and suburban rail network serves the Copenhagen metropolitan area and connects the city center with the suburbs.

A relatively new metro system, Shenzhen is the sixth city in China to open an underground. It has 111 miles of track and 137 stations.

Possibly one of the most dangerous modern metros to construct in terms of life lost, over 100 people have died in the last decade working on various expansions to the network.

One of two separate metro systems used by the citizens of Tokyo, the Tokyo Metro gets so full during peak hours that specially trained individuals known as Oshiya or pushers are used to cram people into crowded trains before they depart the station.

The fourth metro system to be constructed in China after Beijing, Tianjin, and Shanghai, the Guangzhou underground is the sixth busiest in the world and has 120 stations lining 134 miles of track.

With one of the densest metro systems in the world, Paris has 301 stations dotting 133 miles of underground.

Its the second largest metro system in North America after New York City with 195 stations and 140 miles of track.

Although Madrid is only the 50th most populous city in the world, its metro is the 6th longest with 182 miles of track dotted by 300 stations.

After Tokyo and Seoul the Moscow Underground is the third busiest rapid transit system in the world. It has 186 stations lining 192 miles of track.

Short for Schnellbahn or fast train the Berlin S-Bahn has 166 stations along 206 miles of track.