The Delhi Metro is a metro system serving Delhi and its satellite cities of Faridabad, Gurgaon, Noida and Ghaziabad in National Capital Region in India. Delhi Metro is the world's 12th largest metro system in terms of both length and number of stations. A member of the Nova Group of Metros, the network consists of five colour-coded regular lines and the faster Airport Express line, with a total length of serving 160 stations (including 6 on Airport Express line). The system has a mix of underground, at-grade, and elevated stations using both broad-gauge and standard-gauge. The metro has an average daily ridership of 2.4 million passengers, and, as of August 2010, had already carried over 1.25 billion passengers since its inception.