Boston, Massachusetts
The subway system has three rapid transit lines - the Red, Orange and Blue Lines - and two light rail lines - the Green Line and the Ashmont-Mattapan High Speed Line (designated as part of the Red Line). All four colored lines meet downtown at a square configuration, and the Orange and Green Lines (which run parallel) meet directly at two stations.
Moscow, Russia
Moscow Metro (Russian: Московский метрополитен), which spans almost the entire Russian capital, is one of the world's most heavily used metro systems. It is well known for the ornate design of many of its stations, which contain beautiful examples of socialist realist art.
Paris, France
The Paris Métro (French: Métro de Paris) is the rapid transit system in Paris, France. It includes 16 lines, primarily underground, with a total route length of 213 km (133 miles), with 298 stations (382 stops)[1] (245 of these are within the 41 square miles (106 km²) of the City of Paris - the most dense provision of subway stations in the world). Lines are identified by numbers from 1 to 14, with two minor lines, 3bis and 7bis, which were formerly part of their parent line and only later became independent. The system, which has become one of the symbols of Paris, is notable for the density of its network in central Paris, and for its homogeneous architectural style.
New York City, 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 [citation needed], an affiliate of the Metropolitan Transportation Authority and also known as MTA New York City Transit. It is the most extensive public transportation system in the world, with 468 reported passenger stations, (or 422 if stations connected by transfers are counted as one), 229 miles of routes translating into 656 miles (1056 km) of revenue track, and a total of 842 miles (1355 km) including non-revenue trackage. The subway is also notable for being among the few rapid transit systems in the world to run 24 hours a day, 365 days a year. Among the ten busiest systems in the world in terms of annual passenger traffic, it is the only one to hold such a distinction, setting it apart from cities such as London, Paris, Tokyo, and Moscow.
Tokyo, Japan


The Tokyo subway is an integral part of the world's most extensive rapid transit system in a single metropolitan area, Greater Tokyo. While the subway system itself is largely within the city center, the lines extend far out via extensive through services onto suburban railway lines.
Source:
Wikipedia