The viaduct (marked in red) in front of the new terminal building of the airport. A file picture

Once the 1.1km-stretch is dismantled, the rest will be renovated to make it fit for Metro trains. “The overhead power supply set-up has to be replaced by the third-rail power supply system. Metro rakes run on power drawn from the third rail,” a Metro official said.

“The construction of the Dum Dum Cantonment-airport link had started in 2000. Trains started running on the stretch a couple of years later. Initially, nine pairs of trains ran daily. The count was reduced to three and then two pairs. One pair would run in the morning and another in the evening. On most days, the trains would be empty,” an Eastern Railway official said.

Since the viaduct has been lying unused and without any maintenance for years, it has become potentially dangerous and needs to be pulled down, the Metro official said.

A problem that passengers using the suburban train service faced was the distance between the Airport station and the terminal building, which fliers arriving at the airport by train had to cover on foot.

The airport station is being built as a hub, where three lines — from New Garia, Noapara and Barasat — will merge. The original plan was to build the station overground and lay elevated tracks between the airport and Barasat.

But the plan had to be modified because the airport authorities had objected to elevated tracks towards Barasat. After that, the plan to reuse the entire stretch of the viaduct was abandoned.

The railway tracks between the airport and Dum Dum Cantonment, lying unused for four years, and the elevated platform supporting them are being dismantled because lack of upkeep has made the structure “potentially dangerous”, officials said.

The link became functional around 2002, with the Eastern Railway running a few suburban passenger trains till Airport station. But the trains had few takers, prompting the authorities to stop the service on September 30, 2016.

Around 2.1km of the tracks between Dum Dum Cantonment and the airport were laid on a viaduct — an elevated platform.

“A 1.1km stretch of the viaduct from the airport is being dismantled. The rest will be used to run Metro trains between Noapara and the airport,” an Eastern Railway official said.

The tracks will be elevated till the Jessore Road station, where they will move underground. The airport Metro station will be underground.

“Around 100 girders of the viaduct, some along the busy Jessore Road and VIP Road, are to be removed,” said an official of Metro Railway, which is supervising the demolition.

A 600-tonne-capacity crane has been deployed by Metro Railway to remove the girders, each of which weighs between 250 tonnes and 500 tonnes.

“The girders are sliced and clamped with thick strings before being taken off by a crane,” the official said. “The most crucial is the stretch above the crossing of VIP Road and Jessore Road. ”