Prime Minister Narendra Modi will inaugurate the Howrah Maidan-Esplanade section of Calcutta Metro's East-West corridor on Wednesday, heralding India's first venture into underwater metro services, which is deemed as an engineering marvel.

The Howrah Maidan-Esplanade section, a groundbreaking addition to the metropolis' transportation network and touted to be the first transportation tunnel "under any mighty river in India", will have the deepest metro station in the country -- the Howrah Metro station.

Nestled under the Hooghly river, which separates the twin cities of Calcutta and Howrah, this feat stands as a testament to engineering ingenuity.

Calcutta Metro touched a milestone in April 2023 as its rakes completed a trial journey under the bed of Hooghly through a tunnel 32 metre below the water level for the first time in India.

According to researchers, the idea of having an underwater transportation system on the lines of London was first mooted by the British in 1921.

"But the idea did not see the light of the day as soil tests did not yield positive results. They were forced to abandon the idea and the project plan was shelved," Aloke Kumar, Associate Professor of IIM-Calcutta, told PTI.

Kumar, who had conducted extensive research on railways, said the idea was again pushed in the 1980s by then Railway Minister ABA Ghani Khan Chowdhury.

"But the project never saw the light of the day. It was in 2008 after being sanctioned by the UPA government that the construction work began in 2009," a former railway official said.

But political hurdles and cost escalation delayed the project, he said.

Spanning a 4.8-km stretch between Howrah Maidan and Esplanade, it forms a vital segment of the East-West Metro corridor, connecting key areas such as the IT hub Salt Lake Sector V.

According to a statement issued by the Metro Railway, the 4.8-km stretch of East-West Metro from Howrah Maidan to Esplanade has been built at a cost of Rs 4,965 crore.

Of the total 16.6 km of the East-West Metro corridor, 10.8 km is underground, including the tunnel beneath the river.

As a Metro train is expected to traverse the 520-metre stretch under the river in just 45 seconds, it not only offers speed but also ensures a seamless and time-efficient mode of transportation, further enhancing Calcutta's connectivity and urban mobility.

"This corridor, once fully commissioned, will also solve the perennial traffic congestion and improve air quality by reducing carbon footprint," the statement said.

It would also benefit people coming from Hooghly, Howrah and Medinipur as well as other states who would immensely benefit by availing of metro services after getting down at the Howrah railway station.

According to officials, the work for the East-West corridor began in 2009 and tunneling under Hooghly commenced in 2017.

The project has suffered delays owing to an aquifer burst at Bowbazar in central Calcutta on August 31, 2019, leading to severe ground subsidence, the collapse of several buildings there and two more water leakage incidents at the same site in 2022 during tunneling and construction work.

The Salt Lake Sector V to Sealdah stretch of the corridor is commercially operational at present.

The PM will also inaugurate the Kavi Subhash-Hemanta Mukhopadhyay section of the New Garia-Airport Metro and the Taratala-Majerhat Metro section of the Joka-Esplanade Metro.

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