Load limit restrictions were placed on the Shaw River bridge at Yambuk on Monday, with a temporary lane closure on the bridge and a weight restriction of 42.5 tonnes.

Heavy vehicles travelling west will be diverted to the Hamilton-Port Fairy Road and then on to either Woolsthorpe-Heywood Road or Myamyn MacArthur Road.

Those travelling east will be diverted to Tyendarra-Ettrick Road then on to Woolsthorpe-Heywood Road to Hamilton-Port Fairy Road.

Mrs Britnell said the Heywood-Woolsthorpe Road was in no condition to be taking extra heavy vehicles.

"The number of trucks using the road now is creating some issues, so diverting hundreds more trucks that way is going to create a serious safety issue," she said.

"The Heywood-Woolsthorpe Road has large single lane sections, it has steep drop-offs from the edge of the pavement to the shoulders which are full of potholes after recent rain. I have been raising its appalling condition continually for the past three years."

Mrs Britnell said the Princes Highway was a key freight route in and out of the port of Portland, used by hundreds of freight vehicles every day.

"Any diversion is adding time to the trip and in turn adding to the cost of doing business. That impacts everyone, from the transport companies to the producer," she said.

"The minister for roads Jaala Pulford must take immediate steps to rectify these issues as a matter of priority, not only for the safety of south-west motorists, but to help fright businesses keep our produce moving efficiently."

The road diversions were announced after recent structural inspections revealed repairs were required on the Shaw River bridge.

Structural degradation was identified on one of the bridge's supporting piers, which was built in 1952.

Regional Roads Victoria (RRV) chief officer Paul Northey said safety was always the number one priority and temporary traffic arrangements would be put in place to ensure the bridge remained open to as many vehicles as possible.

"A temporary load limit restriction of 42.5 tonnes is in place on the bridge - for the time being heavy vehicles that are over this limit will be detoured via the surrounding arterial road network," he said.

"At the most, the detour will add an extra 30 minutes onto the journey. RRV will also be actively monitoring and inspecting these detour routes."

There are portable traffic lights with radar capacity to control traffic flow, and to ensure no one is waiting too long on a red light.

"We know how important the highway is to the communities and industries that rely on it every day - and we're aware of the impacts these temporary traffic arrangements will have," Mr Northey said.

"We are working as fast as we can to complete detailed structural and geotechnical assessments to guide our repair works on the bridge and will keep the community up to date evey step of the way."

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