The Desert Road between Tūrangi and Waiouru will close for maintenance for two months from Monday.

Waka Kotahi NZTA said the work involved reconstructing 16 kilometres of road, improving drainage, clearing 15 kilometres of road shoulder and replacing the deck of the Mangatoetoenui Bridge.

New bridge deck will add 50 years to its lifespan

Regional manager of maintenance and operations in Waikato-Bay of Plenty, Roger Brady, said the bridge was built in 1966 and in need of replacement.

"This job alone would require the road to have been closed for about a month, so being able to do this at the same time as the other maintenance work due is a real win," he said.

The new deck for the Mangatoetoenui Bridge had been designed and was being built in Napier, ready to be shipped this week.

It consisted of steel girders and a concrete slab, which would be transported in two sections and then stitched together once on-site.

Once the new deck was in place, the Mangatoetoenui Bridge was expected to last another 50 years before it needed replacing.

The Desert road will be closed from Monday for two months. Photo: Supplied/NZTA

Ground temperatures above 13 degrees needed to carry out work

Brady said the average ground temperatures were analysed during the planning stages, and for work to go ahead it needed be a minimum of 13 degrees.

Overnight minimum temperatures started to drop below zero across the Desert Road from March onwards, meaning the possibility of ground frosts.

"Already the area has experienced snow flurries in January and while these are rare in the summer months, there is more chance of lower temperatures from March onwards," Brady said.

Detour in place

The detour from north to south is via SH41, SH47, SH4, SH49 and then back to SH1 in Waiouru, and adds 30 to 40 minutes to the journey.

NZTA said the speed limit near and through Ohakune would be reduced to 50km/h while the detour was in place, along with additional billboards, signage and police patrols.

The section of road south of the SH1/SH47 intersection (the "soft closure point" shown in orange on the map) to the beginning of the first worksite (south of the Tongariro National Trout Centre) would remain open for visitors to access the Trout Centre, but not SH46.

-RNZ