Adelaide’s iconic Thebarton Theatre has been saved from demolition as the state government reveals its plans to finalise the north-south motorway.

Around 500 homes and businesses were also spared from compulsory acquisition, with a tunnel option being favoured in Tuesday’s state budget.

The biggest road infrastructure in South Australia’s history is estimated to set the state back almost $9 billion and take around 10 years to complete.

Apart from Thebarton Theatre, the tunnel option will also save the Queen of Angels Church, Hindmarsh Cemetery and the Hoffman Brick Kiln.

The final motorway will provide for 78km of non-stop freeway-grade roads from Gawler to Old Noarlunga, eventually linking the Northern and Southern Expressways.

The project is estimated to eventually remove as many as 110,000 vehicles from the busy South Road each day.

The corridor is set to be completed by 2030.