Line 1, or the North–South metro corridor, has a total length of serving 26 stations, of which 15 are underground, 9 are elevated and 2 at-grade. It uses the five foot six inch (1.67 m) broad gauge tracks. It was the first underground railway to be built in India, with the first trains running in October 1984 and the full stretch that had been initially planned completed and operational by February 1995. The southward extension of Line 1 to an elevated corridor from Tollygunge to New Garia was constructed and opened in two phases, Mahanayak Uttam Kumar to Kavi Nazrul in 2009 and Kavi Nazrul to Kavi Subhash in 2010. Another extension constructed was the elevated corridor from Dum Dum to Noapara in 2013. The last extension from Noapara to Dakshineswar opened in 2021, thus completing the Line 1.