The Moscow subway system caters to 3.2 billion riders travelling annually on 12 subway lines to 172 stations.

The Moscow Metro covers approximately 290 km. On an average weekday, the subway itself carries about 8.2 million passengers.

Each subway line is identified by an alphanumeric index (usually consisting of just a number), a name, and a colour. The voice announcement systems refer to lines by name, while in colloquial usage they are mostly referred to by colour.

While most of the Moscow trains run underground, some lines cross bridges overlooking the Moskva and the Yauza Rivers.

Image: People ride the subway with a mobile arts exhibition, called 'Watercolor,' in Moscow. | Photograph: Natalia Kolesnikova/AFP/Getty Images.