Works to upgrade Bratten Bridge on the Lipson-Ungarra Road is on schedule to finish by mid to late July and will add 50 years to the design life to the structure.
Work to upgrade the bridge began on May 18 which once completed will remove existing restrictions on the total mass of vehicles able to use the Lipson to Ungarra Road.
A new highly-reinforced concrete deck has been poured and maintenance and paint work has also been done to the steel structure.
Tumby Bay District Council works and infrastructure manager Damian Windsor said works that were still to be done included installation of new guard rails and pavement reconstruction but the project was on track to be finished by mid to late July.
He said this project was driven by the increased vehicle productivity and higher mass vehicles had put more stress on the structure than it was designed to handle.
"We are strengthening the bridge so it can accommodate heavier vehicles than it could previously," he said.
"We're about three quarters of the way there, a lot of the most intensive works have been completed."
Mr Windsor said the underside and foundation structure still had the original 1960s concrete pour but these works would add 50 years in design life into the overall structure.
The $1 million project was funded from state and federal programs with $800,000 from the federal government's Investment Road and Rail Program and $200,000 from the state government.