The Delhi Metro is a rapid transit system serving Delhi and its satellite cities of Ghaziabad, Faridabad, Gurgaon, Noida, Bahadurgarh and Ballabhgarh, in the National Capital Region of India. It is by far the largest and busiest metro in India, and second oldest after the Kolkata Metro. The network consists of Ten colour-coded lines serving 253 stations with a total length of 348 kilometres (216 mi) [285 stations with a total length of 389 kilometres (242 mi) including Gurgaon Metro and Noida Metro. The system has a mix of underground, at-grade, and elevated stations using both broad-gauge and standard-gauge. Delhi Metro operates over 2,700 trips daily, Delhi Metro Rail Corporation Limited (DMRC), a company with equal equity participation from the Government of India and the Government of Delhi, built and operates the Delhi Metro. DMRC was certified by the United Nations in 2011 as the first metro rail and rail-based system in the world to get carbon credits for reducing greenhouse gas emissions, reducing carbon emission levels in the city by 630,000 tonnes every year. Delhi Metro also interchanges with the Rapid Metro Gurugram (with a shared ticketing system) and Noida Metro. On 22 October 2019, the DMRC took over the operations of the financially troubled Rapid Metro Gurgaon.
