The 57-year-old Tallah bridge, a key link between Calcutta and northern fringes, will be shut down at midnight on January 31 to facilitate its demolition.

Commissioned in 1962, the bridge has lost much of its load-bearing capacity and engineers fear it can collapse any moment.

The engineers’ report prompted the Bengal government to decide to dismantle the bridge and build a new one. Demolition is likely to take around three months.

PWD engineers said men and machines for demolition would move in on Saturday. “In the next few days, they will start pulling down the structure from the Shyambazar-end,” said an engineer.

The demolition will result in large-scale traffic diversions. In some cases the detour will be as long as 6km.

Police officers said congestion was unavoidable because the roads through which vehicles would be diverted were not wide enough for the extra load.

“We will fine-tune the diversion plans after analysing the problem-points over the next few weeks,” a senior officer at Lalbazar said.