In India only Kolkata and New Delhi currently have a metro rail system, but many other Indian cities too will soon have metros. Among them are Bangalore, Hyderabad, Chennai, Goa, Pune, Amrtisar, Jalandhar, Ludhiana, Noida, Thane, Chandigarh, Ahmedabad, and Kochi.

Meanwhile, here are the world's 11 most popular international underground transit systems. . .

1. New York

The New York City Subway is a rapid transit system owned by the City of New York and leased to the New York City Transit Authority. The NYCTA is a subsidiary of Metropolitan Transportation Authority. From 28 stations, when it was founded in October, 1904, it has grown to 462 stations. The subway carries 4.9 million people daily.

It is one of the most extensive public transportation systems in the world, with 369 km of rail route. The subway is also among the few rapid transit systems in the world to run 24 hours a day and 365 days a year.

Image: A worker fixes a subway turnstile at a subway station in New York. | Photograph: Emmanuel Dunanda/AFP/Getty Images).