The damaged section of the N2 at Kaaiman's Pass near George will take four to five months to repair, said the Eden District Municipality on Wednesday.
Eden fire chief Annelize Lamprecht said the loose earth below the road would have to settle before repairs started.
The road was damaged in heavy rains in August.
Lamprecht said a single lane of the road was open to traffic on a stop-go basis, with vehicles being escorted through the damaged section.
She said it took about 30 minutes to get through the damaged section, but this might be a bit quicker soon as officials may reduce the length of the stop-go section.
"It's reasonably stable where the vehicles are driving but the slips are still moving constantly, 3mm an hour... It's below the road but if the slip goes it won't affect the road."
The N2 is the responsibility of the SA National Roads Agency Ltd (Sanral).
Sanral said on its website that the rains caused "major instability problems" in the cuttings and fills in Kaaiman's Pass.
"The combination of abnormal high rainfall over a relative short period and the unfavourable angle of dip of the rock formation in certain cuttings, is the main reason for the major slip currently experienced at a position near Dolphin's Point," said Sanral.
"The slip took away the shoulder and part of a lane of the national road over a distance of approximately 50m."
There is a wait of about 40 minutes at the stop-go section.
Vehicles weighing more than five tons may not use the road, but use the Langkloof R62 instead. Another alternative, the Saasveld road, is undergoing maintenance.
"The repairs and improvement of the unstable areas are due to commence in the next week. It is expected that the slip area will be repaired by means of a concrete retaining structure and the other problem areas by means of the installation of rock anchors and bolts, gabion walls and the application of shotcrete," said Sanral.
The railway line between George and Knysna and a private guest house near Dolphin's Point are on subsiding slip.
"It is expected that the house will be completely destroyed. Substantial repairs will be required to re-open the railway line again," said Sanral.
Other sections of the N2 between George and Knysna are being repaired.
At Wilderness, the westbound carriageway is closed for construction, with two-way traffic on the eastbound section.
At Kleinkrans, the road is being resurfaced. There are no road markings and there is one-way traffic through a daytime stop-go.
At Sedgefield, construction started on Wednesday with daytime one-way traffic.
Between Buffelsbaai and Rheenendal, there is construction on the westbound lanes with two-way traffic on the eastbound section.
From White Bridge to Knysna, there is daytime one-way traffic while debris is cleared and temporary repairs are made. - Sapa