Dramatic drop in traffic on old highway a year on from Transmission Gully

Wednesday, 29 March 2023

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

As the long-delayed, billion-dollar Transmission Gully motorway marks 12 months in use, new data shows drastic changes to how traffic now moves north of Wellington.

The four-lane road bypassed Porirua’s northern suburbs as well as Paekākāriki in the Kapiti Coast, replacing the congestion-prone single carriageway Centennial Highway.

Despite the late arrival and a cost blowout from $850m to $1.25b, the new section of State Highway 1 has been transformative for the local area, with traffic drastically shifting away from two state highways.

Waka Kotahi NZTA portfolio delivery manager Mark McKenzie said roughly 25,000 vehicles used Transmission Gully each day, with volumes increasing since January.

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Transmission Gully heading southbound into Wellington. This particular section bypassed the crash-prone coast road between Pukerua Bay and Paekākāriki.

The bypass had been mooted by various lawmakers for more than 100 years, but John Key’s National government secured funding for the project in 2009.

Construction started in 2014 and finished on March 30, 2022 – two years after it was originally scheduled to open.

Along with the Kapiti Expressway and Wellington’s existing motorways, there is now an unbroken multi-lane highway from the Terrace Tunnel to just north of Ōtaki.

State Highway 58 between Pauatahanui and Paremata has dropped from 19,100 vehicles daily to just 6500.

State Highway 58 west of the new motorway used to carry 19,000 vehicles per day. It now carries less than half that.

Daily traffic levels on old State Highway 1 between Mana Esplanade and Mungavin Avenue have roughly halved, while Paekākāriki to Pukerua Bay has dropped from 25,000 vehicles a day to just 6000.

Crash levels reflect the same pattern. Between March 2021 and Transmission Gully’s opening, there were 151 crashes on State Highway 59, with seven serious injuries and one fatality.

After the motorway opened, that plummeted to 28, with one fatality and one serious injury.

Congestion through towns like Pukerua Bay was a reality for Lower North Island motorists, especially around public holiday weekends.

On Transmission Gully, there have been just 18 crashes with no serious injuries or deaths.

McKenzie attributed much of this to the design of the new road.

“Since Transmission Gully opened, Ventia, the highway operator contracted by Wellington Gateway Partnership, has replaced equivalent to 1.2 km of damaged road safety barriers.

“These barriers have been instrumental in preventing and mitigating head-on and run-off crashes along the highway.”

McKenzie also highlighted the increased resilience of the road, saying Transmission Gully saved the area major disruption when a slip closed State Highway 59 near Pukerua Bay last year.

It also provided extra network resilience and an alternate route when SH59 was closed for slip repairs last year.

Horowhenua mayor Bernie Wanden said his district now felt closer to the capital than ever before.

“Here in Levin, we’re 100km from Wellington city centre. Before the expressways, you’d have all these variables with congestion through all the Kāpiti Coast towns like Waikanae, Paraparaumu and then coming into Porirua.

“With the expressways and Transmission Gully, that means a guaranteed one-hour trip. People come and go without thinking too much about it. It makes Wellington much more accessible to people living here.”