REPLACING a key bridge which carries one of Oxford's busiest roads could cost £40m and cause up to two years of disruption.

Oxfordshire County Council said it needs to replace the Kennington Bridge, which carries the A423, because bearings that support it have worn and there is no cost-effective way of replacing them.

About 53,000 vehicles – including 2,000 lorries and 350 coaches and buses – use the bridge every day.

Engineers have said replacing it is one of the most challenging projects in the county because of the impact the work will have on roads, utilities and the £150m Oxford Flood Alleviation Scheme.

The county council installed supports under the bridge about two years ago.

Replacement is likely to start in 2021 and designs for what will replace the worn-out structure have yet to be completed.

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The bridge will not be fully shut during its replacement – and traffic will be able to drive over it in both directions as contraflows will be put in place.

Yvonne Constance, the county council’s cabinet member for environment, said: “The bridge is an essential part of Oxfordshire’s transport infrastructure and is safe for continued use. Work is being carried out to ensure that it will remain safe while the replacement is designed.

“Replacing the bridge would have always been necessary at some point but previous inspections had suggested that would not be any time soon. We have concluded that bringing forward the replacement is the best way to secure the long-term viability of the strategic road work and delivery of a robust flood alleviation scheme.”

She added: “We fully recognise the impact that the construction will have on the Oxfordshire transport network and residents. We will work with all affected stakeholders so they can plan ahead and help us minimise the impact.”

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Motorists who use the city council’s 1,400 spaces at Redbridge Park and Ride site are likely to end up in traffic when work gets underway, along with the tens of thousands of people who use the Oxford Ring Road every day.

Any diversions could pile more traffic on already saturated routes, including Botley Road.

The bridge was opened in 1965 and contains a Thames Water main and fibre optic cables. Power cables pass overhead and about 360 trains pass under the bridge every day.

The only times the council can request train lines are closed for maintenance are during the Easter and Christmas periods so work will be complicated by those limited working times.

The flood alleviation scheme’s length will eventually be about 5km long – and the bridge work affects about 60m of that.

Joanne Emberson Wines, the director of the Oxford Flood Alleviation Scheme, said: “The scheme partnership is committed to helping better protect people, properties, roads and railways around Oxford from flooding.

“We are working closely with Oxfordshire County Council to determine the best way to coordinate the work needed to the bride with the construction of the Oxford Flood Alleviation Scheme.”

Last month, the county council, the city council and other key Oxford bodies objected to the way the Environment Agency was trying to buy land for the scheme.

The councils, the Midcounties Co-op, Network Rail, Oxford Preservation Trust and University College, Oxford were all landowners fighting compulsory purchase orders along the 5km stretch.

Both city and county councils support the scheme but made ‘technical’ objections to the way the Environment Agency was seeking to buy land.