A $258 million interchange on State Highway 2 at Melling will be built by 2026. (File photo)

A State Highway 2 interchange at Melling will be built by 2026 as part of a $1.35 billion investment in Wellington's transport network.

The Government announcement on Wednesday also included plans for a four-lane highway between Ōtaki and north of Levin by 2029, a $211 million investment in the region's rail network by 2025, and further safety upgrades on SH58 by 2023.

The interchange, which is part of Lower Hutt's RiverLink project and includes a new bridge over the Hutt River, will cost $258m.

Hutt-based Labour MP Ginny Andersen estimated that the interchange would save commuters 5 minutes per trip and up to 50 hours per year. Every working day there were 37,000 journeys taken on the highway, she said.

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Hutt Valley motorists have long been calling for the interchange to replace the traffic light-controlled intersection because of traffic congestion and safety concerns.

ROBERT KITCHIN/STUFF The project will include a new bridge over the Hutt River. (File photo)

Wednesday's announcement comes after the New Zealand Transport Agency said in April it would not even consider funding for the project until 2029 or later.

But in September, the agency approved funding for a resource consent application for the interchange, raising hopes it would go ahead sooner than expected.

The future of the 24 kilometre highway between Ōtaki and north of Levin - the third section of the Kāpiti expressway on SH1 - had been up in the air since the agency said in late 2018 it had no funding allocated to the project.

NEW ZEALAND TRANSPORT AGENCY/SUPPLIED NZTA's preferred design for the interchange. (File photo)

It has now been confirmed construction of the $817m project will start in 2025 and finish in 2029, and include a shared walkway and cycleway.

The $211m investment in the region's rail network will include infrastructure upgrades for Wellington, Wairarapa and Palmerston North, and is part of a $2.8b investment in regional roads and rail.

Work will start later this year and finish in 2025.

NEW ZEALAND TRANSPORT AGENCY/SUPPLIED Funding has also been approved for a four-lane highway between Ōtaki and north of Levin. (File photo)

The second stage of safety improvements on SH58 will cost $59m and start midway through this year. The 5.5km of improvements will be completed by 2023.

A total of $6.8b has been confirmed for transport projects across the country over the next 10 years. Wellington's share is separate to the $6.4b approved for the Let's Get Wellington Moving transport programme.

INTERCHANGE A GAME-CHANGER

Lower Hutt Mayor Campbell Barry said the interchange at Melling would be a game-changer for Hutt Valley commuters, but the biggest benefit was increased flood protection.

The interchange is part of Lower Hutt's $50m RiverLink project, which also involves relocating Melling Station and strengthening the Hutt River stopbanks to prevent flooding.

Designers say an interchange and new bridge are crucial to increase the level of flood protection the area could have.

"This will stop us getting devastated by a flood."

However, the project was not a silver bullet for all of the area's transport problems, with much more investment still needed, Barry said.

Central to that was the proposed Cross Valley Link road, which would connect Seaview on the eastern side of Hutt Valley to SH2 on the western side.

Hutt City Council was developing a business case for that project but no cost or timeframe had been determined.

'GREAT NEWS' FOR COMMUTERS

Andersen said although there had been much talk about the interchange project in recent years, National had never allocated funding to it.

She also described the project as a game-changer, with improved safety and reduced congestion because of the removal of traffic lights.

"This is also great news for the thousands of us who catch the train. We'll have a new relocated station with expanded park-and-ride facilities, taking hundreds more cars off the motorway every working day."

Hutt South MP Chris Bishop said the Melling project was a win-win, and a massive victory for people power.

"National committed to this project in 2017 and National Leader Simon Bridges recommitted to the project last year.

"If elected in September, National will build the new interchange as quickly as possible."

Rimutaka MP Chris Hipkins said with no firm plans having been made by National, promises of the Melling upgrade had never been anything more than a vague promise.

He said Wednesday's funding announcement for Melling, in conjunction with double tracking the Hutt Valley rail line, would make for significantly faster travel between the northern Hutt Valley and Wellington.

Upgrades on SH58 would make it the Hutt's primary connection to Transmission Gully and SH1, the country's main arterial road.

WELLINGTON CITY 'SNUBBED'

Wellington Chamber of Commerce chief executive John Milford said Wednesday's announcement would be a bitter pill to swallow for Wellington ratepayers who will be asked to stump up 40 per cent towards the $6.4b Let's Get Wellington Moving programme.

"It is staggering that we can have a $700m, four-lane road to Marsden Point, but there's nothing for the two-lane road to Wellington Airport.

"The Government is expecting Wellingtonians to stump up with 40 per cent of the cost of basic infrastructure projects like fixing the Basin Reserve and, in a decade's time, a second Mt Victoria tunnel.

"This is not only disappointing to our members but will set back the city's growth at a time when the investment is needed to transform the city into a more compact, liveable city with lower housing costs."

A proposed $270m, four-lane highway between Petone and Grenada also missed out on funding. NZTA said in April the road would need to be redesigned and funding for it would not be considered until 2028.

WELLINGTON TRANSPORT PROJECTS

Melling interchange: $258m, by 2026

Ōtaki to north of Levin highway: $817m, by 2029

Rail network upgrades: $211m, by 2025

SH58 safety upgrades: $59m, by 2023