Macquarie Pass will close for three weeks to allow safety improvement work to be carried out.
The Illawarra Highway on the Pass will shut weekly – between 6am on Monday and 3pm on Friday – from July 24 until August 11, weather permitting.
One lane will open on weekends, with traffic control managing vehicle movements in one direction at a time.
During the closures, detours will be in place via Jamberoo Mountain Road for light vehicles, adding about 10 minutes to journey times between Robertson and Albion Park.
The detour for heavy vehicles will be via the Hume Highway, Picton Road and the M1 Princes Motorway.
Heavy vehicle drivers travelling from the Hume Highway to Albion Park should allow an extra 30 minutes of travel time.
The work involves slope stabilisation, widening of the road shoulders, installing guardrails and replacing drains underneath the road to ensure stormwater can be quickly removed.
Seven work zones have been identified west of the Macquarie Rivulet bridge.
The NSW government has allocated $2.3 million over two years to carry out essential safety improvements on the Pass.