An inspection has revealed the work needed to repair the Tyne Bridge is more extensive than first thought, with refurbishment now expected to take four years.
The rusting bridge, which has not had any major maintenance for more than two decades, is due to undergo a £41m restoration.
Details of the programme are due to be discussed by Newcastle City Council next week.
In order to carry out the work, the bridge, which carries 70,000 vehicles a day, will be reduced to one lane in each direction during the refurbishment.
Gateshead transport chief Councillor John McElroy said: “The impact for our transport network of the work required on the Tyne bridge is going to be very challenging for everyone."
The work, the funding for which was approved in June, will include repairs to the bridge's steelwork, repainting it and replacing joints.
The due date for the maintenance work has been pushed back to late 2023, meaning the potential completion could run very close to the bridge’s centenary year in 2028.
The bridge, which was officially opened on 10 October 1928 by the late Queen Elizabeth's grand-parents, King George V and Queen Mary, is home to the world's furthest inland colony of breeding kittiwakes, with more than 1,000 pairs live on the famous structure and its towers.
Councillor Jane Byrne, cabinet member for transport, said: “The Tyne Bridge is a symbol of home to Geordies all over the world and it is really important that we complete this work and preserve our much-loved bridge for future generations.
“This is a challenging and complex project, due to the sheer size of the bridge, its age and Grade II* listed status, protecting the kittiwake colony from disturbance and the massive scope of work required - which isn’t just the sizeable task of painting it - but a full restoration programme to see the bridge returned to its former glory. As well as managing disruption to traffic on a major gateway to and from the city.
“Early timelines show this could be four years, but we will be working to complete the work hopefully sooner, and we will be working with other authorities and public transport providers to have measures in place to mitigate the impact to the travelling public.”
Newcastle and Gateshead councils said shutting a lane of traffic in either direction during the restoration was required in order to carry the work out safely and to protect workers.
Transport chiefs are exploring “a number of mitigation measures” to ease the resulting traffic congestion – including promoting alternative routes and improving public transport links, a spokesperson for Newcastle City Council said.
Funding will come from the Department for Transport and the Newcastle and Gateshead councils, with the government pledging £35m.
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