The bridge (pictured) links Jedburgh St in Roxburgh to Roxburgh East Rd and Teviot Rd, which leads to Roxburgh East and Millers Flat.
A report to the Central Otago District Council roading committee by project engineer Kevin Furnival said several assessments of the bridge identified continued movement of the concrete abutment walls.
The council put a temporary 20kmh speed limit on the bridge to slow traffic but the walls kept moving.
The report said construction was expected to start in September and would finish by mid-December.
Mr Furnival anticipated the bridge would be closed for three to six weeks.
While the bridge was closed, there would be detours in place across the Roxburgh Dam and Millers Flat bridge.
The council plans to advise the public of the bridge closure 10 days before construction starts.
The project will involve installing a reinforced concrete beam and horizontal tie-backs under the road.
The work will cost $750,000.
The district council is asking the NZ Transport Agency to help fund the work.
-By Tom Kitchin
