The cyclone-closed main route between Northland and Auckland is set to open to two-way traffic by the end of March.

But the highway will have to close again after school holidays finish for major slip repairs, said Waka Kotahi NZ Transport Agency.

State Highway 1 at Brynderwyn Hills, south of Whangārei, has been impacted by slips since bad weather hit Auckland and Northland on January 27.

No sooner had those slips been cleared than the road was hit again by Cyclone Gabrielle, followed by flash flooding which also closed a nearby detour through Mangawhai and Waipū.

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The closure has meant a 130km detour through Dargaville for large trucks, which are unable to use local roads.

The highway was open to northbound traffic only on March 1, with heavy southbound traffic continuing to detour through Dargaville and light vehicles using Mangawhai or Paparoa.

But Waka Kotahi said the highway will open to two-way traffic on March 31, in time for the Easter holidays – which usually sees an increase in visitors to Northland.

“To ensure our local road detours aren’t impacted by high volumes of holiday traffic, both northbound and southbound lanes will open from Friday 31 March in time for the Easter break,” the Thursday afternoon update said.

However, the highway will have to close again later in April, to fix the seven major slips.

Also on SH1 in north Auckland, Dome Valley also has a number of slip repairs under way, although the road is open.

Waka Kotahi said temporary barriers have been installed to shift traffic away from under-slips, with repairs starting on these in the next couple of weeks.

SH1 also remains closed at Mangamuka Gorge, south of Kaitāia, from slips caused by a storm in August 2022.