Kolkata Metro (Line 1)

Kolkata Metro Line 1 is India's first metro system. Construction began in 1972 — at the time, the only operational metros in the world were in London, Paris, Tokyo, New York, and a handful of European capitals. Revenue services began on the Esplanade-Bhowanipore section on 24 October 1984, beating Delhi's first metro line by 18 years.

The Line 1 (now called the Blue Line in the multi-line system) runs roughly north-south for 32.42 km from Dum Dum (north) to Kavi Subhash (south) — covering Kolkata's commercial and residential heart. Most of the original Phase I (Dum Dum-Tollygunge) is underground tunnel built using cut-and-cover construction through Kolkata's notorious soft clay — necessitating extensive dewatering and sheet-pile retention systems. The southern extension to Kavi Subhash (formerly Garia) is mostly elevated viaduct, opened in stages through 2010.

Unlike all subsequent Indian metros (which use standard-gauge), Kolkata Metro Line 1 uses Indian broad-gauge (1,676 mm) with 750 V DC third-rail electrification — a legacy of its origins as a project of Indian Railways rather than as an independent metro authority. This makes Line 1 incompatible with subsequent Kolkata Metro lines (Line 2 East-West, Line 3 New Garia-Airport, etc.) which use standard-gauge.

The system is operated by Metro Railway Kolkata, an Indian Railways zonal subsidiary, with daily ridership averaging 600,000 (down from peak 700,000+ in pre-Covid years). The original Bhel-built rolling stock has been progressively replaced with newer ICF/Bhel air-conditioned trainsets.