Preconstruction history

Ngāti Toa’s settlement of the Pāuatahanui inlet and the Kapiti Coast and beyond stretches back over two hundred years. The valley beside the Horokiri stream was a natural pathway for Ngāti Toa, moving from Pāuatahanui to the coast. Led by Te Rauparaha, Te Rangihaeata, and others Ngāti Toa became the predominant Iwi In the territory from 1820.


The Evening Post* reports that an Otaki MP, William Field, is proposing an inland ‘motor road’ from Paekākāriki to Paremata. It’s the earliest known record of the consideration of a main arterial route over the Wainui Saddle. 

*Papers Past | Newspapers | Evening Post | 7 June 1919 | Transport links with Manawatu ( link)


A 110,000 volt transmission line is laid between Wellington and Mangahao Power Station in Shannon, running through the gully and giving it its name.


Greater Wellington Area Transportation Strategic Study investigates a number of transport solutions for Wellington including public transport initiatives and determines that the inland route (Transmission Gully) was preferrable over an upgrade of the coastal route.


Notice of Requirement sought to include the proposed route through Transmission Gully in District Plans.


Appeals resolved and designation confirmed.


Transit NZ and the Greater Wellington Regional Council (GWRC) consult with the public on the Western Corridor Plan.


The Greater Wellington Regional Council include the Transmission Gully project in their Draft 2007-2016 Regional Land Transport Strategy.

View looking down the Horokiri Valley towards Battle Hill Farm Forest Park before construction began.


Preliminary geotechnical assessments begin.


Scheme Assessment Report is completed.

Drilling work in the Te Puka stream valley north of Pouāwhā, the Wainui Saddle looking towards Kāpiti.


Transmission Gully announced as part of the Wellington Northern Corridor Roads of National Significance.

Phase II Environmental and Engineering studies commence.


Scheme design for consents finalised and Assessment of Environmental Effects prepared.


Lodgement of consent applications and Notices of Requirement for designations. Referred to a Board of Inquiry as a project of national significance for determination.

2011/Early 2012

The consenting process commences.

June 2012

Designation and consents for the construction of the Transmission Gully motorway and associated link roads granted.

November 2012

Decision announced that the Transmission Gully project will be delivered as New Zealand’s first roading Public Private Partnership.


Wellington Gateway Partnership consortium announced as the successful Contractor, with subcontractors Leighton (now CPB) HEB JV responsible for the design and construction and Ventia responsible for the subsequent operations and maintenance.  

July 2014

PPP Contract signed.

Construction begins


The Transmission Gully site office at Lanes Flat in Pāuatahanui is established. Enabling works begin and the relocation of utilities gets underway.

Digger heading south along Transmission Gully before the 110kV powerlines are removed by Transpower.


Access tracks and site compounds are created along the route.

Access track at the southern end of the project. Whitby and Pāuatahanui in the background.

Environmental controls are established across the project, and monitoring and control works are put in place.

Harvesting of 40 hectares of the Ranui pine plantation begins.

Native lizards from the Upper Te Puka stream captured and subsequently rehomed in purpose-built lizard-friendly boulder fields.

Native fish, eels and koura are relocated from the Te Puka and Horokiri streams ahead of temporary works for the first of around 7 kilometres of stream diversions.

Major earthworks start across the 27-kilometre alignment.

November – The Kaikoura earthquake hits, followed by a season of heavy rain, delaying construction.


Work gets underway on a number of the project’s major structures, including the largest structure – Te Ara a Toa, the bridge over Cannons Creek.

A 220 tonne crawler crane at work on the foundations for the piers which will hold up Te Ara a Toa, the bridge over Cannons Creek.

Construction begins on the interchanges.

Steel girder bridge installation over the North Island main trunk rail line at Kenepuru, December 2017.

The project’s largest earth cuts start at Pouāwha, the Wainui Saddle.

Duck Creek and Pāuatahanui stream diversions are completed. Landscaping and planting begins.

Noise and retaining walls are installed at the Linden section of SH1, ahead of significant works to replace the Collins Avenue bridge.

Construction begins on a new Southbound Collins Avenue overbridge.


The first launch of the large steel girders for the superstructure of Te Ara a Toa, the bridge over Cannons Creek is successfully completed. In total, four separate launches were needed to complete the deck structure, concluding in 2019.

SH58 interchange construction, December 2018.

The State Highway 58 Interchange structures are completed and works begin on the connection with the Mackays Crossing Interchange.

The team celebrates the completion and transition of traffic over the new southbound section of Collins Avenue Bridge on SH1, and safe demolition of the old section of Collins Avenue Bridge.

The project receives an International Erosion Control Australasia (IECA) award for environmental excellence, for implementing an innovative and environmentally responsible method to manage the challenges associated with constructing a four-lane motorway through the middle of a valley, containing streams with high ecological values.


A massive 2.4 million cubic metres is moved over the 2018/2019 summer season, and well over 6 million hours of work is recorded by April 2019.

By the end of 2019, 14 kilometres of the new motorway is at pre-pavement level, and 89% of the project’s structures are completed, including the bridges for the Waitangirua and Kenepuru interchanges.

Pavement construction begins.

Work to build the northbound flyover connection from Kenepuru onto Transmission Gully, and the middle section of the new Collins Avenue overbridge in Linden, involves lifting 47 beams over SH1.

The project’s innovative in-crane GPS warning system takes out the category win for ‘Best use of innovative New Zealand design or technology to eliminate or manage a risk’ at the 2019 New Zealand Workplace Health and Safety awards.

More than 1.4 million native trees and shrubs are planted across the project in 2019. In total the project will plant nearly 2.5 million native trees and plants, creating one of the most significant lowland native bush areas in the region.


In March the country goes into Level 4 lockdown in response to COVID-19. All construction on Transmission Gully stops for a month. The project faces ongoing challenges due to the complexities of an international workforce, a disrupted nationwide supply chain, and a tightly programmed schedule of works impacted by loss of the crucial pre-winter period.

Paving works recommence with a new localisation strategy for construction, drawing on New Zealand crews and resources.

A temporary asphalt plant is established at Mackays Crossing to supply paving for the northern end of the project.

Project partners, local Iwi, Ngāti Toa Rangatira gift names to key structures on the road.

The project’s largest structure, Te Ara a Toa, the bridge over Cannons Creek is completed. Suppliers Eastbridge Engineering win a national excellence award at the annual Steel Construction NZ Excellence in Steel Awards.

Te Ara a Toa, the bridge over Cannons Creek, stands 60 metres above the stream below.

The Linden artwall is installed on SH1. The design was created in collaboration with artists from local iwi, Ngāti Toa.

By the end of 2020, Construction is 88% complete. A total and 9.6 million work hours has now been recorded on the project and over10 million cubic metres of earth has been moved, bringing the earthworks to 98% completion. It’s one of the largest volumes of earth to be moved on a New Zealand construction project.


It’s the year to put the icing on the cake! The paving that is.

The paving on Transmission Gully is made up of granular pavements (with both chip seal and asphaltic concrete surfacing) and structural (deep lift) asphalt pavements. 

A grader shapes the aggregates to the desired shape and level.

By the end of June, the project is 95% through the construction programme, with asphalt teams placing 13,000 tonnes of asphalt in June.

Compacting deep lift asphalt, which is used in high traffic areas and steep sections of the motorway.

The side and median barriers are completed, road signs are erected, and the radar system is installed and powered. The radar system is similar to systems used in the UK and Europe and detects incidents such as stopped vehicles, vehicles going the wrong way, or animals or debris on the motorway. Transmission Gully is the first motorway in New Zealand to use this technology.

A new building housing Ventia, the company which will operate and maintain the motorway for the next 25 years, is established at Lanes Flat Pāuatahanui.

In August the Order in Council declaring Transmission Gully a motorway is signed by Governor General Dame Patsy Reddy

A few days later on August 18 the Delta variant of COVID-19 strikes the country, prompting a nationwide lockdown  – closing the entire site down for two weeks. Ongoing disruption due to Level 3 and Level 2 restrictions are further complicated by supply chain constraints as a result of the extended lockdown in Auckland.

Despite the impact of COVID-19, the project moves at pace to complete road works, including the ongoing construction of the pavements, barriers, ITS equipment, lighting, line marking and signage.

Two massive full-width gantries are installed on SH1 at both ends of the new motorway, Linden in the south and Mackays Crossing in the north.

The gantries use steel trusses to span the full width of the motorway.  The gantries will hold green directional (guidance) signs, (electronic) variable message signs and other Intelligent Traffic System devices.

The gantry installation work involved full overnight closures of SH1 at Linden and Mackays Crossing and required the use of a crane to lift the 34 metre long, 30 tonne gantries into place.

Late 2021 and early 2022 are focused on meeting the 100 safety and quality assurance tests contractually required for road opening.

By 10 December 2021 only 41 final test submissions had been received from CPB HEB, of which 34 had been accepted by the Independent Reviewer as meeting the required specifications.

Waka Kotahi, Wellington Gateway Partnership, CPB HEB and Ventia negotiate how best to address some of the outstanding issues in order to get the road open to the public as quickly as possible while ensuring the enduring safety and quality of the road is not compromised.

March 2022, an agreement is reached enabling the road to open earlier than otherwise possible.

Transmission Gully by the numbers (at road opening)

  • 27 kilometres long
  • More than 12 million work hours to complete construction
  • 11.4 million cubic metres of earth excavated/moved
  • 660,000 tonnes of aggregate brought to site
  • 104,000 cubic metres of concrete used.
  • 7,900 tonnes of reinforcing steel used in bridges and other structures
  • Over 115,000 tonnes of asphalt laid
  • 25 bridges and large culverts, all built to withstand a 1 in 2500 year earthquake
  • Longest bridge: Te Ara a Toa – 230 metres
  • Highest bridge: Te Ara a Toa – 60 metres
  • Largest cutting: Pouāwhā – Wainui Saddle – 70 metres deep
  • 534 hectares of ecological mitigation and replanting (includes planting 2.5 million native trees and plants)
  • Eight major streams modified/diverted
  • At least 27km of streams protected by planting to provide shade and improve stream habitat   
  • Over the course of the construction around 7,700 people have worked on site.*

* Personnel figures include sub-contractors and everyone from ecologists to digger drivers to cleaners. If we included the people who have worked off-site (such as suppliers, designers and steel fabricators) the number would greatly exceed this.

Before and After – looking north towards Cannons Creek (photo credit Al Grant)

Before, looking north.

After, looking north.

Before and After - Pouāwhā / Wainui Saddle looking south Nov 2015, 2020 and 2021 (photo credit Al Grant)

November 2015