Faulty chip seal forces two summers of repairs on Transmission Gully

Friday, 29 August 2025

A timelapse video of driving the $1.25 billion Transmission Gully from Paekākāriki to Linden on the first day of opening.

Three years after opening, Transmission Gully motorway is facing a two-summer resurfacing programme, with the original chip seal surface and drainage design unable to cope with high traffic volumes and heavy freight.

The motorway was built under a Public-Private Partnership (PPP) with Wellington Gateway Partnership, which hired CPB and HEB to construct the road.

Urgent repairs will be done this summer with additional sections completed next year, meaning the motorway will see two consecutive summers of major maintenance rather than routine periodic work.

A legal dispute over quality and unfinished work was settled confidentially last year and the PPP was restructured, with Waka Kotahi taking on greater responsibility for completing the project and managing ongoing maintenance.

Quarterly repayments to WGP will continue over the next 25 years, while Australian firm Ventia is contracted to maintain the road.

But the details of the settlement and who will pay for the resurfacing remain under wraps, raising questions about whether taxpayers could end up covering the cost.

Around 20 lane kilometres of State Highway 1 north of Porirua will be resurfaced and rebuilt between October and March, with work then continuing into next summer.

It will focus on the Kenepuru, Waitangirua, and SH58 interchanges, as well as the Battle Hill area, affecting both southbound and northbound lanes.

The original chip seal surfacing has not held up under heavy traffic and freight loads.

Mark Owen, Waka Kotahi regional manager, said the drainage was worse than anticipated, with water seeping in through the chip seal layers and subsoil drains, leading to potholes.

“We're a bit surprised that the drainage maybe not as good as we thought it was going to be, so water has got in … That's why we need to go in there and really belt and braces, address the vulnerable areas, put the drainage right, and then come back with good surfacing. Our aim is to move from chip seal to a more sturdy, stronger, better ride asphalt surface.”

Owen said resurfacing would usually happen in 8-12 year cycles, and that chip seal is more suited to modest traffic volumes.

“Once we get to asphalt, we'd be hoping to get at least 10 years life out of it,” he said.

Crews will work overnight, with some lane closures required and diversions onto SH59, the old route of SH1, he said.

Infrastructure New Zealand chief executive Nick Leggett said it was understandably frustrating for motorists and transport users in the lower North Island.

“New Zealanders expect infrastructure that stands the test of time. By learning from Transmission Gully and applying those lessons, we can deliver better outcomes in future projects,” he said.

The resurfacing and the secrecy around costs and legal settlements put Transport Minister Chris Bishop under pressure to explain how future PPPs will avoid similar problems and protect taxpayers.

National campaigned on building 15 new four-lane highways and Bishop has stressed he wants more private sector financing to pay for major projects.

In a statement he said two independent reviews on the project had informed the Government’s revised PPP framework, released in November 2024.

“PPPs when done well can drive better performance with a stronger focus on whole of life outcomes,” he said.

“New Zealand’s PPP approach has a strong focus on greater outcomes rather than lower cost. This is achieved through the strict use of a ‘willingness to pay’ affordability threshold … [a benchmark price that determines if a PPP will deliver value for money compared to a traditional, non-PPP approach].

“This means that any PPP proposal is expected to and must be able to outperform the counterfactual of non-PPP infrastructure delivery for a commensurate net present cost. This will continue in the new framework.”

Bishop declined to comment on the work programme, referring questions to Waka Kotahi as an operational matter.

An independent post-construction review, published last year, identified several significant flaws and problems.

A primary issue was the affordability threshold was set too low during the procurement phase, effectively under-pricing the complex project and leading to inevitable cost blow-outs.

The country’s complex consenting system also emerged as an “unpriceable risk,” preventing the consortium from meeting expected time and cost benefits and leading to early project stress and strained relationships.

Weak project governance and ineffective decision-making were also recurring problems, partly due to a lack of clear structure and Waka Kotahi's initial “light-on approach”.

The project experienced significant delays, opening about two years late.