Transmission Gully opened to traffic in 2022. Photo / Mark Mitchell
Transport Minister Chris Bishop says it is hard to imagine the Wellington region without Transmission Gully, despite years of debate and litigation over the $1.25 billion motorway project.
“We argued about it for years, and everyone said it was too difficult,” Bishop said at the release of a report into the benefits of the motorway.
The report has found the road shaves an average of nine minutes off trip times, has healthier injury statistics, and delivered $79 million in savings in 2024, despite remaining technically unfinished.
The Infometrics analysis was prepared for Infrastructure New Zealand in partnership with the Porirua, Kāpiti Coast and Wellington councils.
“Travel times are shorter and more reliable throughout the day, for both the new road and the old route. Travel time savings range from a median of five minutes across the day, up to 31 minutes in peak times on the most congested days,” the report said.
Altogether, 1.9 million hours were saved in 2024.
The findings are in line with initial projections from the NZ Transport Agency Waka Kotahi (NZTA), which said the road, when opened, would save commuters an average of about 10 minutes on journeys.
Nobody has died on the stretch of motorway since it opened, and the rate of serious injuries per million vehicles has fallen from 0.6 on the old route to 0.2 on Transmission Gully.
Infometrics principal economist Brad Olsen also spoke of 60 impacts on the motorway’s median barrier, meaning potentially 60 head-on collisions avoided.
While not a full cost-benefit analysis, the report said Transmission Gully had seen savings of $94m, minus $15m for the higher vehicle operating costs because of the higher speeds and hillier routes.
Meanwhile, the population in the surrounding areas has grown since the road opened.
Olsen was with Bishop at the event, with Porirua Mayor Anita Baker, Kāpiti Mayor Janet Holborow, and Wellington city councillor Ben McNulty in place of Wellington Mayor Tory Whanau.
The 27km motorway between Porirua and the Kāpiti Coast has been open since 2022 and is used by almost 25,000 vehicles a day, despite still requiring work for completion.
Plans for Transmission Gully stretch back more than 100 years. Construction officially began in September 2014, when Prime Minister John Key turned the first soil on the project.
It was built under a public-private partnership (PPP) by the Wellington Gateway Partnership (WGP), with NZTA, CPB Contractors and HEB Construction subcontracted to carry out the design and construction.
The road’s opening was down to the wire in March 2022 and was made possible only after NZTA agreed to defer some quality assurance tests until after the opening, and reduced the requirements for others.
After years of budget blowouts and Covid-19 delays, severe weather events, and the Kaikōura earthquake, there was a desire to get the road open and to iron out any problems later.
The incomplete works ended up being the subject of legal action in the High Court after NZTA’s expectation that they should be completed to the standard in the project’s contract.
A settlement in 2024 of these legal disputes means NZTA is now responsible for finishing the road.
The ongoing works come amid a review to increase the speed limit on the motorway to 110km/h.
It was previously due to be considered by NZTA this year, but Newstalk ZB revealed last month that 20km still needs rebuilding, resurfacing, and drainage works.
Works on the stretch north of Porirua are forecast to take six months, planned from October until March, meaning lane closures are likely during the day and full closures at night.
It remains unknown how much these works will cost.
Bishop said these works were “obviously disappointing” but were necessary to ensure the road was properly maintained and fit for the future.
“I’m frustrated by it, and I think Wellingtonians and users of the road will be a bit frustrated by it as well, but look, it is what it is.”
Consultation had now taken place on increasing the speed limit to 110km/h, and he planned to provide an update by the end of the year.
Ethan Manera is a Wellington-based journalist covering Wellington issues, local politics and business in the capital. He can be emailed at ethan.manera@nzme.co.nz.