The 27-kilometre motorway will provide a safer and more reliable transport route between Wellington and the lower and central North Island.
“Waka Kotahi is absolutely committed to getting Transmission Gully open to the public as soon as possible. We know that people are very keen to drive on the new motorway and we’ve made our expectations clear to our Public Private Partnership (PPP) contractor, the Wellington Gateway Partnership (WGP),” says Waka Kotahi General Manager Transport Services Brett Gliddon.
“We understand how anxious motorists are to know when they will be able to drive on the new motorway, and we’re also impatient to see the road open.
“Waka Kotahi wants the road open before the Christmas holidays, but achieving that will depend on the ability of the road’s builder, the CPB HEB Joint Venture, to meet critical requirements necessary to ensure that the road is safe for motorists and completed to a high standard.
“We are monitoring their progress very closely, and we’ll be providing regular updates over the coming weeks so people will know how the work is tracking and understand the scale and complexity of the requirements that need to be met. We expect to announce in mid-December whether the road will open before Christmas or not.”
While construction work has been progressing well since the site was reopened under Alert Level 3, a significant number of critical requirements remain to be met by the CPB HEB JV before the motorway can safely and legally open to the public.
As well as finishing the physical works for the motorway to open, CPB HEB JV also needs to meet a large number of safety and quality tests. These are required by the project agreement, which also requires WGP and the builder to complete environmental compliance requirements to comply with consent conditions before the motorway can open.
There are 100 safety and quality assurance tests that the contract stipulates must be met before the road can open. As of 29 October 2021, 37 final submissions have been received from the builder, of which 25 have been accepted by the Independent Reviewer as meeting the required specifications. However, 21 tests are yet to be submitted and 42 have only been partially submitted.
Some of these tests can’t be completed until the road construction has finished.
There are also 47 consent tasks that WGP and CPB HEB need to complete in order to meet the contractual requirements for road opening. Although 45 of these consent tasks are underway and have been progressed to varying degrees, only three had been fully completed as of 29 October 2021. The remaining 44 tasks will require sign off from Greater Wellington Regional Council (GW) and/or the relevant territorial authorities.
Because of the scale and complexity of the road construction and the PPP contract, there are more tests required than usual to ensure that when the road is finished and open it has been built to the agreed standards. This is crucial to ensure safety and quality and also so that there are no major issues that need to be repaired or redone after it’s opened, which could lead to frustrating closures for road users.
Mr Gliddon says under the PPP contract, it is ultimately the responsibility of WGP and CPB HEB to deliver a road that meets the safety, quality and environmental standards agreed in the project agreement, and expected by the public. Once those standards are met, the PPP contract will move into the service phase – the 25-year maintenance and operations period.
As the PPP contractor for Transmission Gully, WGP has subcontracted CPB HEB to undertake the motorway’s design and construction, and Ventia to operate and maintain the motorway for 25 years, after which it will be handed over to Waka Kotahi at an agreed standard.
Mr Gliddon says PPP agreements are a different model to what has been used for all previous roading projects in New Zealand.
“Transmission Gully is New Zealand’s first transport infrastructure project being delivered under a PPP. The terms of the contract are very strict, both for the build phase and the operation and maintenance of the road. This is how we ensure we are getting what we are paying for in terms of quality, safety and performance over the period of the contract. At the end of the 25-year operating period, responsibility for the road passes to Waka Kotahi.”
Building Transmission Gully – key facts:
- Transmission Gully is one of the largest transport infrastructure projects in New Zealand.
- 27 kilometres of motorway, with four new interchanges, have been built through geologically and geotechnically challenging and steep terrain with constrained and difficult access, requiring construction of 25 major structures (bridges and large culverts).
- All structures have been built to withstand a 1 in 2500-year earthquake. The largest structure, Te Ara a Toa is 230 metres long and 60 metres high.
- Cuts of up to 70 metres were made through the Wainui Saddle, which also has the Ohariu fault line running through it. Pouāwhā Wainui Saddle has been lowered to a final crest height of 253 metres above sea level.
- More than 11 million cubic metres of earth has been moved, the largest volume of earthworks ever undertaken on a roading project in New Zealand. With well over half of the catchment draining into the ecologically significant Porirua harbour, the earthworks required extensive environmental controls including more than 100 sediment retention ponds.
- The road runs through valleys criss-crossed with streams. As part of the project, around seven kilometres of streams have had to be diverted, and approximately 27 kilometres of streams are being restored, with planting along the banks to provide shade, reduce water temperatures, and improve the natural habitat for stream life.
- The Transmission Gully project includes one of the largest native planting programmes undertaken in New Zealand as part of a construction contract, with more than 550 hectares of ecological mitigation areas being either retired from grazing or revegetated.
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