The 16.6-km Kolkata East West Metro will ferry an estimated one million passengers per day by 2035, a senior Railway official said on Wednesday.
The project, to be completed by 2021, will also have the county's first underwater tunnel.
The 520-metre twin tunnel, one east-bound and the other west-bound, is built 30 metres below the riverbed. Commuters between Howrah and Mahakaran metro stations will be under the river for only about a minute when the train passes through the tunnel at a speed of 80 km per hour.
"According to our estimation, by 2035, one million passengers will be using this metro line every day," the official said.
The official also said that a 5-km stretch between Salt Lake and Howrah has already received approval from the Commissioner, Railway Safety, and will be operationalised soon.