Site enabling works on New Zealand's biggest new infrastructure project begin this month.

David Low, Wellington Gateway Partnership chief executive, said initial works on the 27km $850 million Transmission Gully motorway job north of Wellington begin after Anzac Day in New Zealand's first public private partnership for a state highway project.

He described progress.

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"Enabling works during April will include stabilisation trials to confirm the correct methodology is in place to support the transportation of around 6.5 million cubic metres of dirt from cuts to batters and provide monitoring benchmarks to provide assurance of environmental performance in readiness for the high production bulk earthworks that will follow," he said.

Establishment works for the project site office and compound began in December and will be finished this month.

This has involved bringing in more than 29,000 cubic metres of earth from a local quarry to build the site up only 1m, but enough to support relocatable buildings or portacoms across a big area to accommodate up to 120 permanent staff at the peak.

Staff are due to move into the site office in the second quarter of this year and the project will ramp up gradually so that the labour force will peak in the 2015/2016 and 2016/017 periods.

The job is extremely challenging, building a four-lane motorway through some of the steepest and most challenging terrain in the region, dotted with many valleys and sheer hillsides.

The motorway route runs through 11 different types of geological terrain from rugged rocky out crops through to rolling farmland.

Project director Mick O'Dwyer said that terrain presented many challenges which would require many different types of construction techniques and equipment, from bulldozers to mechanical scrapers, diggers and dump trucks.

Midden Excavation at Lanes Flat. Left to right: Reuben Mills, LHJV Senior Environmental Advisor; Malcolm McLeavy, Goodman's digger driver; Mary O'Keeffe, Project Archaeologist. Photo / Mark Tantrum
Midden Excavation at Lanes Flat. Left to right: Reuben Mills, LHJV Senior Environmental Advisor; Malcolm McLeavy, Goodman's digger driver; Mary O'Keeffe, Project Archaeologist. Photo / Mark Tantrum

Matt Lowrie, transport advocate and Transportblog editor, disapproves of the project.

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"It is expected to encourage more people to drive and therefore make other options like the trains less viable. Overall it's a massive project that will cost a lot and lock us into large repayments over long period of time. It's diverted money from more worthwhile projects in other parts of the country," he said.

Nor could it be made a toll road: "Modelling suggested not many would use it in that scenario. That's a good indication that the road probably isn't considered useful enough by people. Also there are questions as to whether that many trucks would use it compared to the coastal route."

The motorway route runs through 11 different types of geological terrain from rugged rocky out crops through to rolling farmland. Photo / Mark Tantrum
The motorway route runs through 11 different types of geological terrain from rugged rocky out crops through to rolling farmland. Photo / Mark Tantrum

Nor is he impressed with the funding arguments.

"In the event of a major earthquake, it's likely that most of the cost of repairing it is likely to sit with the taxpayer. It's been said that in the event of a large earthquake that damages both Transmission Gully and the coastal route, that the coastal route is likely to be faster to repair and get open so it doesn't even provide that much resilience," Lowrie said.

Patrick Reynolds also of Transportblog also disapproved.

Wellington is not growing, traffic is not growing there, very few will use this road especially if tolled, it has an appalling cost benefit, and they are breaking the PAYGO model of road funding we have had working successfully for years by using a PPP. It will be paid for by the next generation, who may not want it.

"Wellington is not growing, traffic is not growing there, very few will use this road especially if tolled, it has an appalling cost benefit, and they are breaking the PAYGO model of road funding we have had working successfully for years by using a PPP. It will be paid for by the next generation, who may not want it," Reynolds said.

Low said design development work was ongoing and the motorway was part of a much bigger national project.

"Design work is a critical element of the project in terms of the delivery of a safe, seismically resilient, aesthetically pleasing and low maintenance motorway that will be an integral component of the 110km Wellington Northern Corridor Road of National Significance," he said.

Because environmental monitoring will be a key focus, divers Keith Gregor and David Guccione from the Bay of Plenty Polytechnic have been undertaking marine surveying. Photo / Mark Tantrum
Because environmental monitoring will be a key focus, divers Keith Gregor and David Guccione from the Bay of Plenty Polytechnic have been undertaking marine surveying. Photo / Mark Tantrum

Adherence to environmental and regulatory consenting processes have been a big focus.

Because environmental monitoring will be a key focus, divers from the Bay of Plenty Polytechnic have been undertaking marine surveying of the Pauatahanui inlet. Data collected from 10 pre-determined sites will be used to manage work during the construction phase, Low said.

Environmental management will result in the construction of 7km of swales, 17km of silt fences, 37km of dirty water diversions and 26km of stream enhancement or mitigation works.

The Wellington Gateway Partnership is funding, designing, building the motorway. It will then operate and maintain it for the 25 years following the five-year build period. The motorway is due to open for traffic by 2020.

The Government will make regular payments to the partnership and, at the end of the 25-year operations and maintenance phase, the partnership will hand the motorway over to the Government to run and maintain.

The winning partnership beat the Positive Connection bid, made up of John Laing Investments and Fletcher Construction.