But, in news that will disappoint Illawarra motorists, stage one will be at the northern end of the long-awaited road project.

It has long been suspected that the extension would start at the northern end and head south, as it is the sections closer to Sydney that need more immediate relief from traffic congestion.

The first stage of the extension is proposed as a four-kilometre twin tunnel with a height of 5.3 metres, which will run from the WestConnex New M5 junction at Arncliffe to President Avenue in Kogarah.

It is estimated the project will see motorists skip as many as 23 sets of traffic lights.

“Anyone who drives through this area knows how congested these roads are and how vital this link will be, which is why we are progressing with planning for Stage 1 of the F6 extension,” NSW Premier Gladys Berejiklian said.

Ms Berejiklian announced on Tuesday that $35 million would be committed for planning and development work.

This was on top of the $15 million already in the state budget.

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READ MORE: F6 extension to cost $20 a day in tolls

The Premier said a final design for the tunnel and costing would not be known until mid-2018.

NSW Roads Minister Melinda Pavey said the property impacts for stage one “will be low, compared to other major road projects”.

Roads and Maritime Services will continue early investigations along the remainder of the proposed F6 extension route.

Feedback on the proposed tunnel can be left on the Roads and Maritime Services website.