Only eastbound traffic will be able to cross Tewantin's Doonella Bridge from Monday 6 July to early December with westbound traffic subject to a detour.
This six-month change is necessary as Noosa Council contractors upgrade the 68-year-old bridge to extend its life by another 50 years.
They need to close one lane of the bridge so this essential work can be carried out.
"This means you can cross Doonella Bridge by car to get from Tewantin into Noosaville, but to drive back into Tewantin from Noosaville, you'll need to detour via Goodchap Street, Eumundi Noosa Road and Beckmans Road," Council's Infrastructure Services Director Shaun Walsh said.
Mr Walsh said traffic modelling showed a one-way flow of traffic eastbound over the bridge with a westbound detour would create far less congestion and delays than having east and westbound traffic share one lane of the bridge in a stop-go arrangement.
"A stop-go arrangement across the bridge would likely create traffic backlogs of up to 3 km long on either side of the bridge," he said.
"There will still be delays and congestion with the westbound detour approach - that's unavoidable when upgrading a major link that carries 20,000 vehicles a day - but this option will minimise the impacts as much as we can.
Unfortunately, these works are unavoidable and need to be completed," he said.
Mr Walsh encouraged anyone who was able to ride a bike or take a bus to do so for the duration of the bridge works.
"As with emergency vehicles, public buses - and school buses - will still be able to travel westbound across the bridge, with special traffic lights in place to allow them quickly across, so public transport is a great alternative to taking the car," he said.
"Pedestrians and cyclists will also continue to have safe access via the shared bridge pathway.
"We appreciate our community's patience while these essential works are completed to ensure this bridge continues to serve our shire for at least another 50 years," Mr Walsh said.
"Traffic impacts are unavoidable, so we ask motorists to allow extra travel time, have patience and please consider carpooling, walking and cycling wherever possible, or take a bus."
The bridge upgrade includes structural strengthening, new safety barriers, repairing underwater bridge piles and improving the Hilton Terrace approach.
"There will be some aspects of the work carried out at night as much as possible to help minimise impacts on traffic during daytime hours, as well as reduce the period of work,"
Marine access beneath the bridge will be closed during the entire project.
The bridge upgrade is jointly funded by the Australian Government's Safer Local Roads and Infrastructure Program, in partnership with Noosa Council.
