Transmission Gully was officially opened in 2022. (File photo) Photo: RNZ / Angus Dreaver
Shorter travels times and less roading deaths are among the benefits of Transmission Gully a new report has found.
The report by Infometrics, which was commissioned by Infrastructure NZ, looked at the economic and social benefits of recently built highways Transmission Gully and the Kāpiti Expressways (Mackays to Peka Peka and Peka Peka to Ōtaki).
Shorter travel times on new roads
The report which analysed TomTom travel time data estimated travel time savings on the Transmission Gully ranged from a median of 5 minutes across
the day, to 31 minutes at peak times.
Travel time savings on Mackays to Peka Peka meanwhile ranged from a median 5 minutes across the day, to 21 minutes in peak times.
Peka Peka to Ōtaki meanwhile was estimated to save road users an average of 5 minutes.
Altogether, the report estimated the new roads saved road users 3.8m hours in travel time in 2024, which was valued at being worth $187m.
Transmission Gully. (File photo) Photo: Mark Coote
Reductions in deaths and serious injuries
The new roads have been designed and constructed to significantly higher safety standards than the old routes and no deaths have been recorded on any of the three new roads since they opened.
For Mackays to Peka Peka and Peka Peka to Ōtaki, no deaths have been recorded on the old route after the new road opened, suggesting that reduced traffic volumes have reduced the likelihood of crashes.
However, since Transmission Gully opened, several fatal crashes have occurred on the old route (SH59), despite a significant reduction in traffic volumes.
"As time goes on, one might expect the annual number of fatalities on SH59 to reduce, and there may be deaths on the new roads," the report said.
"Mackays to Peka Peka has a much longer operating record (seven years) than Transmission Gully and Peka Peka to Ōtaki (three years), so as time goes on the trends should become clearer and long-term averages less disrupted by variation."
Serious injury rates were also down since the new roads had been built.
Roads bring population centres closer together
The report said the new roads have changed accessibility within the region, effectively bringing population centres closer to central business districts (CBD), adding scale to existing CBD.
"The most pronounced effect of the new roads is on the Porirua CBD, which has an additional 74,400 people within a 60-minute driving time, a 15 percent increase."
Population in Horowhenua, Kāpiti, and parts of Porirua which were directly connected to Transmission Gully had also grown significantly faster since 2010 than the Hutt
Valley or Wellington.
With the roads making Porirua and Kāpiti closer in terms of travel time, the opening of Transmission Gully was associated with a material change in house prices within
the region.
"Regression analysis shows that the gap closed by $63,400 between September 2022 and March 2025," the report said.
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