The Transport Agency says it will probably be early next year before the road through the Manawatu Gorge is reopened.
State Highway Three has been closed since 31 August - the longest closure since 2004 - forcing traffic between Manawatu and Wairarapa to use the more roundabout Pahiatua Track and Saddle Road routes.
Heavy rain on the night of 18 August brought down about 1000 cubic metres of soil and debris, blocking the road about two kilometres from the Ashhurst end of the gorge.
One lane was cleared for traffic on 28 August but three days later another slip blocked the road again. A further major slip followed in October.
The Transport Agency's regional state highways manager, David McGonigal, says the plan is to get heavy machinery to the top of the slip and dig out two terraces.
He says workers will then be able to clear away the loose material and assess the damage to the road and bridges.
Mr McGonigal says the whole process is likely to take about two months to complete.