Contractors are about to start a complex operation on State Highway 25, just south of Coromandel town, which will allow heavy vehicles to use an area affected by a slip below the road.

The slip below the road, which occurred on August 10, has restricted traffic to a single lane and trucks have been excluded due to the unstable nature of the site.

A geotechnical inspection of an underslip on State Highway 25 south of the Coromandel township will be taking place today. Photo: NZTA

The New Zealand Transport Agency's regional performance manager Karen Boyt says geotechnical reports and a lot of planning has been undertaken to find a solution.

'The work to be done will involve using an excavator to dig out the bank beside the road. This requires careful planning and attention to achieve the right outcome, which will enable us to shift traffic onto a safer alignment.

'The solution will mean all traffic will now be able to use the road.”

Weather permitting, the work is expected to start on Thursday and the road should be open to all traffic on Monday.

This will continue to operate as one-lane with signals controlling traffic until the permanent solution can be constructed.

The Transport Agency appreciates the patience of road users, particularly freight operators and their clients who have been affected by the detour.

Motorists can expect delays of up to ten minutes while the excavation work is taking place. Drivers will be stopped during parts of the operation and traffic flows will be monitored to lessen the impact on motorists.

Heavy vehicles can use State Highway 25A as an alternative route.

Work is continuing with geo-technical engineers to find a permanent solution for the site. More information on this is expected next week.