The closure of bridge 135 across the Taieri River on Hyde-Macraes Rd is expected to cause major disruption on the well-used road until September.
Strath-Taieri Community Board chairman Barry Williams said the road was the most direct sealed link between the Hyde-Ranfurly and Macraes-Dunback areas.
The bridge was used daily by farmers whose properties straddle the Taieri River, school buses, rural mail contractors, parents taking children to schools further afield, workers getting to the Macraes mine, people needing to pick up supplies in Middlemarch and transport operators, among others.
The shortest detour, via Middlemarch and a partially unsealed road through Moonlight, added 50km to the trip, while the shortest fully sealed option, via Kyeburn and the Pigroot, added about 70km.
Dunedin City Council project engineer Evan Matheson said the annual check on the bridge earlier this year showed the 1879 bridge's timber supporting beams on both ends had deteriorated badly.
A weight restriction was immediately placed on the bridge.
He said the council had weighed up replacing the beams against leaving the restriction in place, but on further consideration it was decided the beams were in danger of failing, so a decision was taken to fix them.
The $407,000 project, including the replacement of the bridge's deck while the contractors are there, is expected to take up to three months.
Alexandra company Breen Construction won the tender and will start work on Monday.
Asked why the beams appeared suddenly to be in such bad condition, Mr Matheson said council staff would look into why the problem was not picked up earlier.
He believed the bridge was the oldest in the council's area. He said the council was conscious it was a ''life-line'' bridge and arrangements had been made with the contractor to allow for people to walk across the bridge during the project, meaning people could leave a vehicle on each side, and there had been indications some would do that.
School buses would also come to the bridge and turn back.
Hendy Cook, from Cook Transport at Hyde, said company trucks crossed the bridge regularly.
A ford across the river had been used since the weight restriction was imposed, but with higher river levels during winter, drivers would have to use the detours while the bridge was closed.
He was pleased, however, the work was going to be done relatively quickly.
''It's a bit awkward, but at least we're getting it done.''
Jocelyn and David Kinney's farm straddles the river. Mrs Kinney said they would get by, but she was concerned many people were unaware of the closure.
Mr Matheson said he had been in contact with some affected people.
Mr Williams said there had been several on-site meetings about the project.
''My main concern is that people coming from further afield, like the Maniototo, will not realise before they get here that they can't get across,'' Mr Williams said.
Breen Construction would erect signs at the Dunback and SH87 ends of the road, advising the bridge was closed.
It was hoped the work would take less than three months.
