Major works have begun to replace the aging Spring Hill Creek bridge, near Mena Park on the Beaufort-Carngham road in Pyrenees shire.
The road will be closed for about four months.
A detour is now in place, using Trawalla Road and the Western Highway, until at least late July.
Pyrenees shire chief executive Jim Nolan said the existing bridge dated back to the 1960's and didn't meet modern engineering standards.
"Without these improvements strict load limits would need to be introduced and a range of vehicles could not use the bridge," he said.
The new bridge would be able to carry high-mass vehicles and would feature improved safety rails.
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"The scale of this project means that the detour along Trawalla Road will need to be in place for several months," Mr Nolan said.
"We will be doing everything we can to minimize the disruption and complete the works by the end of July, weather permitting."
The $970,000 project is part of ongoing infrastructure upgrades by Pyrenees shire with funding assistance from the federal government's Roads to Recovery program.
