Cars and smaller vehicles headed towards Red Road and Strand Road from Brabourne Road will be diverted through East-West Metro's Mahakaran station courtyard from Thursday.
The East-West Metro authorities have covered up about 4m of a lane of Old Court House Street with tin sheets to complete some remaining construction work at Mahakaran station.
Police said the diversion is to ease congestion that may arise out of this.
"This work will not hamper the running of trains (starting on March 15). But we need to block the area for this," said an official of Kolkata Metro Rail Corporation (KMRC), the implementing agency of East-West Metro.
Signage has been put up on the station's courtyard directing vehicles to either head straight from Brabourne Road near Writers' Buildings or take a left turn on Old Court House Street.
A preliminary survey of the arrangements has been completed to ensure there are no hiccups after the start of the Howrah Maidan-Esplanade Metro service.
"A portion of a lane of Old Court House Street will remain covered with tin sheets for the next 40 days. This means some of the road space will be lost. This would pose challenges because traffic here is heavy throughout the day," said a traffic officer.
A KMRC official said the barricading was required to complete the work of clearing space for constructing a covered drainage shaft and a footpath along the Mahakaran station. "A part of the work of sprucing up the area has been completed. The area has been cleaned up and covered with a concrete layer. We want to finish the remaining work within this time frame," said the official.
Traffic headed towards Red Road down Old Court House Street from Brabourne Road comprises buses, minibuses, goods and smaller vehicles, including cars.
"We have decided to segregate smaller vehicles and break them into two parts. Those headed straight towards Red Road from Brabourne Road will move down the courtyard and take a left turn to reach Old Court House Street," an officer said.
"Smaller vehicles headed towards Telephone Bhavan and Strand Road from Brabourne Road will head straight and take a left turn," the officer said.