With work delayed on the new culvert to replace the Whakaruatapu Bridge north of Dannevirke, the new road will not be open until December, rather than May as earlier indicated.
"From April to May our contractors have made good progress forming the new road alignment and the pavement is being steadily progressed with the intention that the section north of the bridge will be completed before winter sets in," a New Zealand Transport Agency (NZTA) spokesperson said.
"However, while we were originally aiming for traffic to be able to use the new road and culvert by May, the combination of bad weather and unexpected geotechnical challenges means work on the culvert has taken longer than expected."
From a geotechnical perspective, the site has been challenging, with the bedding steeply inclined and constantly varied materials.
In some areas, the road is as much as 11m lower than the existing road and through this depth the material has varied from pit metal, to sand, to weak silts, hard papa and a young, fragile black coal.
To counteract the varied materials, the contractor has needed to complete additional ground improvements, while some cut slopes have had to be re-cut at flatter angles because of very weak layers.
With the work weather-sensitive, contractors will not work on the culvert over winter but will return to the site in October.
"It is expected the road over the culvert will be able to be used from early December when the existing bridge will be demolished and further landscaping and tidy-up work will take place throughout December and January," the NZTA spokesperson said.
Tararua Mayor Roly Ellis said he was not surprised by the delays.
"You can't defeat the weather and such a massive project as this in a very big dip is going to be affected by the weather," he told the Dannevirke News.
"It's far better to do it once and do it properly."
However, Mr Ellis said he believed everyone would be glad to see the metal at the north end of Whakaruatapu Bridge, known to locals as "the skinny bridge", sealed.
"I would also like to see the 70km/h signs at either side of the existing bridge remain in place, as they help prevent accidents as people rubberneck to try and get a better view of the work.
"And while delays are to be expected, it's been a great achievement to get the money for this project and to see it well under way."
Excavated material from the new road alignment is being used to build up the road over the new culvert, with the new road position easily seen from State Highway 2. Approximately 40,000cu m of earth has been removed from the site to increase visibility for safety on the new alignment, and much of it has been done overnight to reduce the impact of the work on road users.
The NZTA spokesperson said the aim had been to reduce delays for road users wherever possible. "We appreciate the courtesy and understanding motorists travelling through the site have shown."