The 27km Transmission Gully motorway north of Wellington has been designed specifically to withstand an earthquake.

Paying to use the Transmission Gully motorway is creeping closer to reality after the Transport Minister was warned the $852 million road north of Wellington could make driving too attractive.

A briefing document from the New Zealand Transport Agency to Transport Minister Phil Twyford, released to Stuff under the Official Information Act, recommended he green-light investigation of a Transmission Gully toll to "shape demand" for the new four-lane expressway, which will connect northern Wellington to the Kāpiti Coast when it opens in 2020.

Twyford has since confirmed he gave the recommendation his blessing. This signals a significant lane-change for the Labour Party, which did not publicly support the idea of a toll when it was in Opposition.

BRADEN FASTIER/STUFF Transport Minister Phil Twyford has noted NZTA's investigation into tolling Transmission Gully and agreed it should continue its work developing a potential proposal.

The Transport Agency briefing document says tolling the 27-kilometre gully motorway would help make the main commuter route between Wellington and Kāpiti more "mode neutral", meaning everyone does not simply drive.

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When open, the motorway was expected to reduce the cost of road travel, which would encourage more people to get into their cars at the expense of public transport, primarily rail, the document said.

NZTA Progress along Transmission Gully north of Wellington City, which should be completed by mid-2020. (File photo)

"Tolls could counter the perceived cost reductions of travelling by road."

Tolls were an important part of the transport agency's toolkit because they provided an extra source of revenue, the document said. They were also useful for transitioning New Zealand towards a more "responsive" pricing system.

"Tolling gets people used to paying as they travel, and paying extra for certain benfits."

SUPPLIED Other examples of tolled roads include the Northern Gateway Toll Road, along SH1 at Auckland, which uses a camera gantry system. (File photo)

Twyford told Stuff he was not opposed to tolling roads if it was the right option for a particular project.

"We were critical of the previous Government's financing of Transmission Gully through a public-private partnership because it increased costs over the life of the project," he said.

"Now that the project is going ahead under the former Government's arrangements, it may make sense to establish a revenue source to off-set some of those costs."

NEVILLE MARRINER/STUFF The NZTA will continue its work on a proposal to toll drivers using Transmission Gully, similar to the system used north of Auckland. (File Photo)

The previous National Government inked a deal with a business consortium in 2014 to have the motorway built by the private sector. Once it is opens to traffic, the agency will begin paying it off, along with interest, maintenance and operating costs, in annual instalments of $125m over 25 years.

But Twyford's position appears somewhat at odds with what Labour was saying during negotiations to form the current Government back in October, when he said the party's then-transport spokesman Michael Wood said they did not support tolling the motorway.

"My understanding is that past modelling has shown that a toll on Transmission Gully risks making the road so poorly used that it defeats the purpose of building it in the first place," Wood said at the time.

STUFF National List MP Brett Hudson believes the Public Private Partnership structure for Transmission Gully meant "that this critical piece of infrastructure could be delivered with savings over a traditional procurement model and without the need for tolling."

National's associate transport spokesman Brett Hudson said a Transmission Gully toll would be a rough pill for Wellingtonians to swallow on top of the recently-annouced petrol excise tax increase and the Wellington regional council's desire for a regional fuel tax like Auckland's.

"Wellingtonians and other inter-regional travellers understood the [funding] model would remove a requirement for tolling, and to have the new Government come in halfway through the build, effectively threatening to whack our hardworking taxpayers even more, is disappointing."

Automobile Association spokesman Mike Noon said he wanted to see the "maximum amount" of traffic using the new, safer motorway, and the idea of discouraging drivers from using it would be like "a safety own-goal".

"It's pretty dumb when you've put the infrastructure in."

Porirua Mayor Mike Tana said he was against a toll "because that would guarantee fewer cars and the removal of large freight trucks from our local roads".

"We would not like to see Porirua people having to pay tolls."

The country's three existing toll roads – the Northern Gateway north of Auckland, the Tauranga Eastern Link, and the Takitimu Drive toll road near Tauranga – charge about $2 per car and $5 per truck.

* This story has been corrected. An earlier version of the story quoted Phil Twyford as saying: "My understanding is that past modelling has shown that a toll on Transmission Gully risks making the road so poorly used that it defeats the purpose of building it in the first place." It was Labour's former transport spokesman Michael Wood who said this.

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