The flank of the Parama flyover that takes vehicles from EM Bypass to Park Circus will be closed to traffic at night for a month beginning April 28.

The lane will be shut from 11pm to 6am until May 27 to facilitate repair of the expansion joints, Kolkata Police said.

An expansion joint is a gap between the two deck slabs of a bridge, which allows room for expansion and contraction of the slabs with temperature variations. A mild steel structure in the expansion joint at the Parama flyover helps absorb this expansion and contraction, structural engineers said.

The Kolkata Metropolitan Development Authority (KMDA), which maintains the 7.5km-long flyover, will do the repairs. KMDA engineers said this will be the first time in nearly 10 years that the flyover’s expansion joints will be replaced.

“The late-night traffic is comparatively less, and arrangements have been made to divert the vehicles towards Park Circus and AJC Bose Road. The traffic block has been given considering that the traffic volume is less between 11pm and 6am. Officers have been instructed to ensure there are no glitches,” Yeilwad Shrikant Jagannathrao, deputy police commissioner (traffic), told Metro.

Senior officers said the night diversion plan that has been drawn up for a month will take vehicles from EM Bypass towards the Park Circus Connector, along No. 4 bridge, towards New Park Street and Congress Exhibition Road to reach Amir Ali Avenue. Vehicles headed towards AJC Bose Road will move further west, towards Nasiruddin Road before reaching the AJC Bose Road flyover.

“This will come into force from April 28 and go on till May 27,” the notification issued by city police chief Manoj Verma said. The KMDA engineers said the seal covers of the flyover’s expansion joints will be replaced by experts.

“Just as fish plates on railway tracks help distribute the load through expansion joints, the seal covers of the expansion joints on bridges and flyovers help carry the load from one stretch to another,” a KMDA engineer said.

“This replacement job is vital for the longevity of the Parama flyover.”