The Nene Bridge which carries the A1139 Frank Perkins Parkway, over the River Nene and railway line, needs its bearings replaced to prevent the structure from becoming unsafe.
Bridge bearings are designed to transfer the loads between the main structure and its supporting features.
The bridge, which is near the Embankment, is a major traffic route but also provides a route for pedestrians and cyclists to go between the north and south of the city.
Funding for the project has previously been allocated from the council’s capital budget to be spent between 2015 and 2025.
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The works are expected to begin sometime in April and take 18 months to complete.
A Peterborough City Council spokesman said: “The majority of work will be carried out under the bridge to the supporting piers which will not impact on motorists during the day.
“However, a number of overnight closures to the parkway are planned so that the bridge can be jacked up at each pier location.
“We anticipate having 12 overnight closures and these aren’t expected to start until the autumn at the earliest.”
The project is to be carried out by Skanska which has had a contract for highways services in Peterborough since October 2013. The council said a decision to put the contract out to the open market would “incur additional costs and delay the start of the works.”
The bridge was first constructed by the Peterborough Development Corporation in 1984.
The council has previously been criticised over another bridge - Rhubarb - which sits over the A47/A15 junction near Brotherhood Shopping Park. The authority had planned to knock the bridge down and replace it with pedestrian crossings, but council leader Cllr John Holdich guaranteed last December that there would be a bridge there long-term.