Delhi Metro is a rapid transit

Rapid transit

A rapid transit, underground, subway, elevated railway, metro or metropolitan railway system is an electric passenger railway in an urban area with a high capacity and frequency, and grade separation from other traffic. Rapid transit systems are typically located either in underground tunnels or on...

 system serving Delhi

Delhi

Delhi , officially National Capital Territory of Delhi , is the largest metropolis by area and the second-largest by population in India, next to Mumbai. It is the eighth largest metropolis in the world by population with 16,753,265 inhabitants in the Territory at the 2011 Census...

, Gurgaon

Gurgaon

Gurgaon is the second largest city in the Indian state of Haryana. Gurgaon is the industrial and financial center of Haryana. It is located 30 km south of national capital New Delhi, about 10 kilometers from Dwarka Sub City and 268 km south of Chandigarh, the state capital...

, Noida

Noida

Noida , short for the New Okhla Industrial Development Area, is an area in India under the management of the New Okhla Industrial Development Authority . Noida came into administrative existence on 17 April 1976 and celebrates 17 April as "Noida Day". It was set up as part of an urbanization...

 and Ghaziabad in the National Capital Region

National Capital Region (India)

The National Capital Region in India is a name for the conurbation or metropolitan area which encompasses the entire National Capital Territory of Delhi as well as urban areas ringing it in neighbouring states of Haryana, Uttarakhand, Uttar Pradesh and Rajasthan...

 of India

India

India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

. It is one of the largest metro networks in the world. The network consists of six lines with a total length of 189.63 kilometres (117.8 mi) with 142 stations of which 35 are underground. It has a combination of elevated, at-grade and underground lines and uses both broad gauge

Broad gauge

Broad-gauge railways use a track gauge greater than the standard gauge of .- List :For list see: List of broad gauges, by gauge and country- History :...

 and standard gauge

Standard gauge

The standard gauge is a widely-used track gauge . Approximately 60% of the world's existing railway lines are built to this gauge...

 rolling stock.