The Princes Highway Corridor Strategy studied the 422-kilometre stretch of the road from Yallah to the Victorian border.

The report identifies starting construction of the new Shoalhaven River crossing is a "short term priority”.

This is in large part due to the issues facing the southbound bridge, which is more than a century old.

“This is a heritage-listed iron truss bridge dating back to 1881,” the report stated.

“The deck of this bridge has a limited life under vehicular traffic loads and cannot realistically be rehabilitated under current traffic conditions.”

The iron trusses also limit the height of vehicles that can use the bridge, and can increase the risk of a closure due to an accident.

“Should a major incident occur preventing access across the Shoalhaven River, including access via the adjacent northbound bridge, extensive detours would be required,” the report noted.

These detours, including the Nowra-Moss Vale Road and Hume Highway would add “hundreds of kilometres to a journey”.

The report also found that work on a third crossing is the “most significant action” that can be taken to improve traffic flow through Nowra and plan for future traffic growth.

“In the light of all of these concerns, management of the issues associated with this bridge is considered one of the highest priority challenges within the Princes Highway corridor,” it stated.

“Work is currently under way to develop a third crossing over the Shoalhaven River as an alternative to this bridge.”