Ticket to ride: World's 10 most popular metro systems

A rapid transit, underground, subway, elevated railway, metro or metropolitan railway system is an electric passenger railway in an urban area. They are either located underground or on elevated rails above street level. Across the world, metros are considered as cheapest and fastest mode of transport.

In India, Kolkata, New Delhi and Bangalore have a metro rail system in place, and work is underway in many other cities like Mumbai.

Meanwhile, here is a list compiled by CNN Go on world's 10 most popular metro systems.

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Guangzhou, China

Guangzhou Metro operates 144 stations, including 14 interchange stations and 236 km of tracks.

Guangzhou's first metro line was opened in 1997 and the second line was opened in 2002, making it the fourth city in Mainland China with an underground railway system after Beijing, Tianjin and Shanghai.

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Tokyo, Japan

Tokyo's rail system runs across 102 train lines and over 14 billion passengers ride the metro every year. Thus, making it the most used subway system in the world in terms of annual passenger rides.

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New York City Subway

It is one of the oldest and most extensive public transportation systems in the world. The system's stations are located throughout the boroughs of Manhattan, Brooklyn, Queens and the Bronx. Staten Island has a rail line, the Staten Island Railway, which opened in 1860. The New York City's MTA runs 24 hours a day.

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Madrid, Spain

The Madrid Metro system is the sixth longest metro in the world.

Madrid's railway serves 1.5 billion passengers each year with 21 lines and 396 stations.

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Montreal

The Metro was inaugurated on October 14, 1966. Originally it consisted of 26 stations on three separate lines. Today, the Metro incorporates 68 stations on four lines measuring 69.2 km in length, serving the north, east, and centre of the Island of Montreal.

In 2014, it is expected to add 468 new train carriages, replacing more than half of the older cars.

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Paris, France

Paris has one of the densest metro networks in the world with 245 stations in 14 lines, and in just 87 kilometres of the city. It is not just the densest metro, but it is also the fifth busiest with over 1.5 billion passengers a year.

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Sao Paulo, Brazil

Sao Paulo Metro is the main rapid-transit system in the city of Sao Paulo and the largest in Brazil. It is also the second largest system in South America and the third largest in Latin America, behind Mexico City and Santiago.

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London, England

The London Tube was the world's first underground metro. Opened in 1863, it serves 270 stations and has 402 kilometres of track, 45 per cent of which is underground. It is the second largest metro system in the world in terms of route miles.

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Singapore

The Mass Rapid Transit or MRT as it is popular known in Singapore, is the second-oldest metro system in Southeast Asia. The network has since grown rapidly with an average daily ridership of 2.406 million as of 2011.

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Copenhagen, Denmark

Copenhagen Metro runs a driverless rail system. It is just 10 years old, and has two lines. The metro runs 24 hours and serves 22 stations.