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.
Brady said the average ground temperatures were analysed during the planning stages, and for work to go ahead it needed be a minimum of 13C.
Overnight minimum temperatures started to drop below zero across the Desert Rd 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.
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.