Delhi Metro is a metro system serving Delhi, Gurgaon, Noida, and Ghaziabad in the National Capital Region of India.Delhi Metro is the world's thirteenth largest metro system in terms of length and a member of Nova Group of Metros. Delhi Metro is India's third urban mass rapid transportation system, after the Kolkata Metro and Chennai MRTS.
As of October 2014, the network consists of five colour-coded lines (Red, Blue, Green, Yellow, Violet), plus a sixth Airport Express line, with a total length of 193 kilometres (120 mi), serving 140 stations (with 6 more Airport Express stations), of which 38 are underground, five are at-grade, and the rest are elevated. All stations have escalators, elevators, and tactile tiles to guide the visually impaired from station entrances to trains.
It has a combination of elevated, at-grade, and underground lines, and uses both broad gauge and standard gauge rolling stock. Four types of rolling stock are used: Mitsubishi Rotem broad gauge, Bombardier Movia, Mitsubishi Rotem standard gauge, and CAF Beasain standard gauge.