$620m Manawatū to Hawke's Bay highway pushed back until mid-2025

The opening date of the new highway between Manawatū and Hawke's Bay has been delayed until mid-2025.

The $620 million replacement for the shut road through the Manawatū Gorge, Te Ahu a Turanga, was expected to be finished in late 2024.

But problems in the ground where foundations for two 300m bridges at the Palmerston North-Ashhurst end of the project, and Covid-19 complications, have pushed that back.

Since the old State Highway 3 through the gorge shut permanently because of rock fall in 2017, motorists travelling between the east and west of the lower North Island have been forced over the slow and windy Saddle Rd or Pahīatua Track.

Project alliance owner interface manager Grant Kauri confirmed the new expected opening date during a media tour of the construction site on Monday.

"We're now looking at a time of mid-2025, primarily due to a lot of the challenges that we've faced across the project, [including] the high artesian water pressure and being unable to get a good start on our piling on bridge 2," he said, having previously confirmed to RNZ the late-2024 opening date was under review.

"[And] Covid and the real impacts that's had on us in terms of shutdown and supply chain issues -that commutative effect has pushed us out a further six months."

It was too soon to say what effect the new date would have on the project's cost, but that was under assessment, Kauri said.

Construction on the new 11.5km, four-lane road began more than two years ago after the wider region had waited for many years for a more resilient east-west route not affected by slips, as the gorge road was.

From the Palmerston North end, at Ashhurst, the new road wends over the two bridges, before climbing a steep cut in the lower Ruahine Range.

One bridge, an "eco-viaduct" over a wetland, had an unusually large amount of artesian ground water where its piles went, Kauri said.

"We had to eliminate the water, because if we started piling when the water was still there it would just be coming out of the ground and make it unworkable."

Huge 30-to-40m concrete spans were now appearing in place on the viaduct.

They were made in Napier and were hauled to the site in the early hours so not to disrupt traffic, Kauri said.

The Parahaki Bridge, over the Manawatū River, also presented unexpected challenges where its piles went.

This structure would be among the final parts of the new road to finish, in early 2025, and would include a look-out for the shared bike and walking track next to the new road, Kauri said.

Its piers were undamaged during Cyclone Gabrielle, although there was minor damage to the temporary structures being used in its construction.

"With the water that's coming from the other side, the Manawatū River was a natural funnel for a lot of that water to come through," Kauri said.

"We experienced a high volume of water, the highest level since the 2004 floods."

With that came debris - mostly logs, which caused the minor damage.

Further up the lower slopes of the Ruahine Range, the landscape is changing dramatically on the windy peaks that house a wind farm.

"Our total earthworks across the project are 6m cubic metres," Kauri said.

"We've moved just a scratch over 5.2m cubic metres. We're nearing the completion of these earthworks."

He said they would be finished ahead of time.

The route carved out from massive cut into the hillside is starting to look like a road.

"We're doing pavement trials now, and also on the Ashhurst side you can see us building our pavement and getting that prepped up, making some good inroads there."

The curving climb, below high terraces, looks like the Transmission Gully road, north of Wellington, and it's just as steep.

At the top among the turbines, "zone 3" has also proven tricky in places due to the wetness of the ground, but the road's path is clearly visible.

At the Hawke's Bay-Woodville end, the road begins at the intersection of where the old SH3 meets the beginnings of Saddle Rd.