No deaths, $173m saved: The benefits of Transmission Gully and Kāpiti expressways
Friday, 19 September 2025
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No deaths, fewer serious injuries, and $173 million in costs saved a year: a report card for Transmission Gully and Kāpiti expressways shows serious improvement for Wellington residents.
The analysis of the economic and social benefits of the billion-dollar expressways north of Wellington City, provided to The Post, was produced by Infometrics for sector group Infrastructure New Zealand and the Wellington, Kāpiti and Porirua councils.
The economists at Infometrics determined the three expressways ‒ Transmission Gully, Mackays to Peka Peka, and Peka Peka to Ōtaki ‒ saved travellers 3.8 million hours of driving time in 2024, put 74,000 more of the population within 60 minutes’ drive of the Porirua city centre, and closed a gap in house prices between Wellington city and the rest of the region by $63,000.
Evidence of the benefits of roads has been welcomed by Infrastructure New Zealand chief executive Nick Leggett, Porirua mayor Anita Baker and Kāpiti mayor Janet Holborow, who want to see more efforts to connect the region - and the country.
“Get on with Levin. Get on with Petone to Grenada and the Mt Vic tunnels. But also, across the country, look at mass transit in Auckland, look at the second harbour crossing, look at State Highway 1 Canterbury to Ashburton,” Leggett said.
“It's about all forms of transport working together as a combined network, as a … grower of the economy and enhancer of people's daily lives.”
Leggett said the report should be “a bit of a wake up call” for government agencies, which did not sufficiently evaluate the long-term benefits of infrastructure after it is in place.
It has been three years since the $1.25 billion Transmission Gully and $445m Peka Peka to Ōtaki expressway were opened. The $630m Mackays to Peka Peka expressway opened in 2017.
The routes have meant greater north-south travel in the region, with the combined traffic for both the old highways and new expressways exceeding the traffic in 2015.
Infometrics used TomTom travel data, which it said is also used by NZTA, to determine that Transmission Gully saved on average nine minutes travel time for northbound drivers, and as much as 13 minutes southbound and 37 minutes northbound during peak times, compared with the old Centennial Highway route.
This made for 1.9 million hours saved in 2024. There had also been no deaths on the road between 2022 and 2024, and the rate of serious injuries per million vehicles had fallen from 0.6 to 0.2.
Using NZTA’s methodology to quantify such benefits in dollar terms, the report estimated this made for a combined benefit of $79m in 2024.
Travel time savings would have been $94m but were offset by $15m for increased vehicle operating costs due to the higher speeds and hillier route.
There were similar findings for the Mackays to Peka Peka expressway, at a $63m benefit in 2024, and the Peka Peka to Ōtaki expressway, at a $31m benefit. Both expressways have also had no deaths.
The overall benefit in 2024 from the three roads estimated at $173m.
Holborow, the Kāpiti mayor, said the reduction in travel times and sharp reduction in injuries and deaths were “really welcome news”.
“We're looking forward to the road to Levin to increase our connectivity to Levin, and also through to Palmerston North alongside the new trains that have just been confirmed,” she said.
Other benefits included greater accessibility across the region, the “most pronounced effect” being for the Porirua city centre which now has more than 74,000 people living within 60 minutes’ drive, a 15% increase.
Baker, the Porirua mayor, said the statistics were better than she thought they would be.
“We've obviously got a lot of businesses that have come to Porirua, or are still even coming, because of … Transmission Gully. It's made a huge difference to the inner bit of our city,” she said.
“We've got more housing going into Plimmerton and to Pukerua Bay. But we don't now have that traffic.”
There has also been population growth exceeding that of other parts of the Wellington region. The areas of Horowhenua, Kāpiti and Porirua directly impacted by the roads grew by 22% between 2010 and 2024, whereas the Hutt Valley grew 14% and Wellington City 10%.
In that growth area, the price of houses also closed on Wellington City priced by $63,400, which Infometrics called “a statistically significant change”.
The report also tallied the cost of upgrades in the two decades preceding the new expressways, including underpasses, clearways and safety upgrades totalling $75m, adjusting for inflation.
This money ‒ a mere portion of the total costs of the expressways ‒ may not have needed to be spent, if the new roads had been built sooner.
Baker said she now wanted a Petone to Grenada North highway built.
“It makes us one region, instead of just being split little cities.”