The twin cities of Kolkata and Howrah, on either side of river Hooghly, will be soon connected by a metro service, part of which runs under water. The first tunnel connecting Howrah and Kolkata is ready.

How long did it take?

On March 22, a German-made tunnel-boring machine, christened Prerna, punched through the diaphragm of the proposed Metro station at Esplanade in Kolkata and came out on the surface of the earth. It marked the completion of an eventful journey of 23 months from April 21, 2016, when the machine was lowered into the ground on the other side of the river. Another tunnel-boring machine Rachna, running parallel to Prerna, is catching up and is just a few metres behind.

What’s the distance under water?

Having traversed a distance of 520 metres below the riverbed, the two tunnels, about 3.8 km long, are the first underwater transport tunnels in India. The depth of the crown of the tunnel below the riverbed is 13 metres. Experts who oversaw the construction of the engineering marvel say the challenge was not only boring the tunnel below the riverbed but taking it past some of the oldest buildings in Kolkata, two Jewish synagogues, the Raj Bhavan and a few dilapidated Railway buildings which could not even be evacuated.

Why are the tunnels needed?

The tunnels are the most crucial part of the East West Metro Project, a 16.6-km line connecting Salt Lake in the north-eastern fringes of Kolkata to Howrah Maidan on the other side of the river. Of the 16.6-km line, about 10.8 km will be underground and the rest will be through an elevated corridor.

The mega infrastructure project, costing ₹8,474.98 crore, was delayed primarily by objections raised by the Archaeological Survey of India to a 3.8-km stretch running too close to three heritage structures. With the construction of these tunnels being almost over, work on the project has received a major boost.

What’s the plan?

Work on the next phase of the project, construction of tunnels connecting Esplanade to the Sealdah railway station, will begin in May.

Once this phase is complete, two of the busiest railway stations, Sealdah and Howrah, located on the opposite banks of the Hooghly, will be connected. Kolkata Metro Rail, the agency executing the mega project, is hopeful that by 2021 metro services will be operational along the entire route.

Why is it important for the city?

The East West Metro Line will align with the existing 27.23-km North South Line, which ferries 6 lakh passengers on a weekday. This was the first metro railway in the country and has been operational since 1984.

Considering the population growth, it is projected that by 2035, 10 lakh passengers will take the East West Metro daily. Among major Indian metros, the ratio of road space to city space in Kolkata is the lowest, at 6%. The only hope for the lumbering traffic system, suffering from want of road space, is the metro railway networks criss-crossing the city. Along with the East West Metro project, four metro networks are in the pipeline.