New highway to replace Gorge route

Since the closure of SH3 through the Manawatu Gorge due to large slips the local councils, businesses and road users have waited somewhat impatiently for a replacement route to be announced. The new route has been greeted with both optimism and frustration. Richard Silcock reports.

IN MID-MARCH the New Zealand Transport Agency finally revealed its long-awaited preferred option for a new section of SH3 to replace the Manawatu Gorge route which has been closed to traffic since April last year due to massive slips.

Paving a section of the Saddle Road using hot-mix asphalt. Maintenance work has required closure at narrow sections of the secondary alternative routes from time to time.

This closure effectively resulted in the Manawatu, Hawke’s Bay and Wairarapa/Tararua regions being cut-off from each other. It forced road users to travel the alternative, narrow, steep and windy Pahiatua Track or Saddle Road routes which were never intended to carry heavy traffic volumes and are themselves prone to closures.

The Transport Agency’s director of regional relationships, Emma Speight says that following thorough investigation and extensive consultation, Option 3 of the four shortlisted options under consideration (refer Contractor Dec/Jan 2018) had been selected as the safest and most resilient route.

This option would see a new bridge and a new section of highway constructed from the Te Apiti wind farm viewing carpark on the western (Palmerston North) side of the Ruahine and Tararua Ranges across to Woodville on the eastern side of the ranges.

It will be a ‘greenfields’ alignment well to the north of the gorge and will cross over the Ruahine Range which provides greater ground stability conditions than the gorge route which is on the Tararua Range side of the river.

In making the decision, the agency says it selected this option because it also best balances the cost and the combined needs of the local communities, businesses and road users.

“It will re-establish key strategic transport and freight links that support the needs of the people and economies of central New Zealand,” says Emma.

This new section of SH3, which it is estimated will cost between $350 and $450 million to construct, will be 12.4 kilometres long and pass through the Te Apiti wind farm. It will take four years to complete once all the preparatory work has been finalised.

“A detailed business case for the new route is being worked on,” says Emma. “The next step will be to develop the design to a sufficient level of detail to support applications for the required approvals and we anticipate being ready to start construction in early 2020 with completion by 2024.”

This new section of highway will have an average incline gradient of 5.8 percent, with a maximum of eight percent (similar to Wellington’s Ngaraunga Gorge).

This is well below the alternative Saddle Road, which has a gradient of 16 percent in places and has been undergoing fairly extensive upgrading and maintenance at a cost of near $10 million. This has included constructing five passing bays, patching shoulders, and widening and resealing in an effort to cater for the additional traffic now having to use it as the main east-west route.

This has entailed nearly 71,000 square metres of new paving, and 66,089 cubic metres of soil cut-to-waste and 38,502 cubic metres of cut-to-fill.   

Stringfellows Contracting is carrying out this upgrade and Higgins the maintenance work for the Tararua District Council which is responsible for the road. It is expected this work will be completed by the middle of this month.

Compared to the gorge, travel times on the new route are expected to be reduced by up to three or four minutes and could save up to 20 minutes when compared to the alternative Saddle Road and Pahiatua routes.

The announcement of the new route has been largely welcomed by local councils, businesses in the region and the local communities.

“The ongoing instability (and huge slips across the highway) of the gorge route, which ultimately led to its closure has caused huge disruption for the region,” says Tararua District mayor, Tracey Collis.

“A new route has been a matter of priority for local councils and it is pleasing to have worked so constructively with the Transport Agency to reach a decision that addresses both the immediate issue and the longer term strategic issues for the region.”

Shopkeepers in Woodville along with transport operators, while delighted with the news, are disappointed it is going to take so long to construct.

“Six years is a long time for a community which relies on people coming through the town for their trade,” says Woodville shop manager Sera Williams. “We have definitely noticed a huge difference in the amount of traffic [not] coming through the town since the gorge was closed.”

Likewise transport operator, Glenn Carroll says he is not looking forward to another six years of having to use the alternative routes, as his trucks move between the Manawatu and Hawke’s Bay up to six times a day.

“The Saddle is often closed [for ongoing maintenance] and going via Pahiatua is a pain in the neck as it adds to [travel] time and also costs significantly more.”

Wairarapa MP, Alistair Scott concurred, saying in a statement in a local paper that the decision to go ahead with Option 3 is a good one, but that the six-year wait would “continue to frustrate the region”.

“There’s going to be opportunities lost because of the disconnection between east and west,” he says.

“It does seem like a bloody long time, and it always takes longer than expected!”

In making the announcement on the new route, Emma Speight said the agency is also committed to advancing investigations for a regional freight ring-road which stakeholders see as a critical part of the package for unlocking regional and economic development across the region.

Horizons Regional Council chair, Bruce Gordon says that progressing a regional freight ring-road ‘in parallel’ with the new highway would be a significant step forward for the region.

“It would connect key freight hubs and bring significant improvements to freight and passenger vehicle movements through the hub of the Manawatu by improving travel times and lowering costs,” says Bruce in a statement to local media.

The slips that resulted in the Manawatu Gorge highway being closed in April last year saw 15,000 cubic metres of rock and earth straddle the highway and crash into the Manawatu River far below. Following extensive geotechnical investigations the road was deemed too dangerous for road crews and equipment to operate safely in an effort to clear the highway as the cliff faces were highly unstable and showed continual movement and cracking.

While perhaps not the most ‘creative’ solution in finding an alternative to the gorge route (there were several ideas floated, ranging in cost of up to $2.5 billion and encompassing ideas such as a viaduct set above and along the river bed, a tunnel, or a deep box cut through the gorge), it does offer a solution at minimal cost and provide a more direct route, albeit in six years’ time.


This article was first published in Contractor‘s May issue.

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