Kolkata Metro East-West (Line 2)

Kolkata Metro East-West (Line 2, Green Line) is India's first metro line to cross under a major river — a 520 m twin-tube tunnel under the Hooghly river connecting Howrah Maidan to Esplanade. Inaugurated by Prime Minister Modi on 6 March 2024, the underwater tunnel is the engineering centrepiece of a 16.6 km East-West corridor connecting Salt Lake (eastern Kolkata IT hub) to Howrah (the railway hub on the west bank of the Hooghly).

The tunnel was excavated by two Herrenknecht TBMs ('Prerna' and 'Rachna') with cutter heads operating 32 m below the riverbed. The TBMs operated under 4 bar of water + soil pressure — among the highest pressures any Indian TBM has worked under. Tunnel lining is precast segmental rings of high-strength concrete. The overall depth means the tunnel passes 13 m below the deepest dredged channel of the Hooghly, providing clear navigation for cargo ships above.

Kolkata Metro Rail Corporation (KMRC) — a 50:50 joint venture of Indian Railways and Government of West Bengal — executed the project at ₹8,985 crore. JICA funded 65% via soft loans. Civil construction began in 2009 but encountered chronic land-acquisition disputes in central Kolkata's heritage zone (multiple British-era buildings had to be underpinned), pushing the original 2014 schedule by 10 years.

The line uses standard-gauge (1,435 mm) — incompatible with the older Line 1 broad-gauge but compatible with all newer Indian metros. Rolling stock is BEML-built 6-coach trainsets. Daily ridership has scaled to 80,000 in the months after underwater section opening, projected to reach 600,000 at full network maturity.