This drone footage taken between 7.30am and 8am illustrates traffic before and after the Waterview tunnel opened.

Who proposed the Waterview Tunnel on Auckland's motorway system? That's the $1.4 billion or $2.7b question, depending who you ask.

The National Party was front and centre claiming responsibility for the tunnel after Monday night's Newshub debate, prompting a Twitter exchange between Helen Clark and Steven Joyce.

Both claimed ownership of the idea, with Joyce saying National "called it in," made it a lane wider, and delivered it $1b under what Clark's government would have.

TWITTER/SCREENSHOT Helen Clark reentered the New Zealand political fray to claim credit for the Waterview Tunnel project on Tuesday.

And govt that called it in w new RMA rules, built it, made it a lane wider in each direction & spent $1Bn less on it that planned is this 1 — Steven Joyce (@stevenljoyce) September 4, 2017

READ MORE:

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* Truth or fable? Fact-checking the second leaders debate

* Billion-dollar Auckland tunnel canned

DID JOYCE 'CALL IT IN'?

NZTA/SCREENSHOT A cut and cover alternative to Clark's tunnel was proposed in May 2009, but abandoned by December.

Eventually. But not without first calling it off.

In the last year of the Clark government, Labour approved a two-by-two lane 4.5 kilometre tunnel, running underneath Clark's former electorate of Mt Albert.

After the Key government came to power in November 2008, then-Transport Minister Steven Joyce announced his preferred option was to ditch bored tunnels in favour of a cheaper route combining a surface route with cut and cover tunnels that could be expanded to a three-lane route further down the track.

NZTA/SCREENSHOT Soon after Joyce became Transport Minister, NZTA released cost assessments comparing a surface tunnel with Clark's proposal.

The government also came under pressure to fund infrastructure projects outside of Auckland.

Bill English's own brother, Conor English, Federated Farmers chief executive at the time, said the tunnel project was unwarranted and the money saved could be used for irrigation projects instead.

"We don't disagree that a road should be built but why not save the extra billion dollars it takes to build a tunnel," Conor said.

But Joyce's plan would be revised later in 2009, after massive opposition from Waterview residents.

The Waterview Tunnel as Aucklanders know it now runs along a remarkably similar route to the original proposal approved by Clark's government, comprising two three-lane tunnels, stretching 2.5km.

But Joyce did make the Western Ring Route a "Road of National Significance", meaning it only needed to be approved by the Environmental Protection Authority, fast-tracking its approval by bypassing resource consent processes.

WIDER AND CHEAPER?



The Waterview tunnel is a three-lane twin-bored tunnel that cost $1.4b.

It is certainly a lane wider than the Clark government's initial proposal, but was it delivered for $1b less as Joyce claimed?

Well, it depends how you divide costs between the Western Ring Route and the Waterview Tunnel, and on that the numbers are not clear.

In 2009, NZTA made a presentation claiming the Clark government proposal would cost $2.77b for twin two-lane bored tunnels or $3.1b for a three-lane version.

But this number included improvements to State Highways 20 and 16, and it is not clear if the cost can be directly compared to the government's headline cost for the tunnel itself of $1.4b.

A fairer comparison could be to the cost of the entire Western Ring Route, which NZTA has priced at $2.4b.

According to Matt Lowrie of Greater Auckland, an influential website about Auckland transport issues, the Manukau Harbour crossing and a stretch of road up to Maioro St in Mt. Roskill - which are part of the Western Ring Route - were already under construction before Joyce decided to build the Waterview tunnel as we know it now.

However, Joyce has a defence in this regard as the billions required for the Waterview Tunnel and Western Ring Route were not set aside by the Clark government, according to what NZTA said in 2009, which was why Joyce said he looked at a cheaper option in the first place.

And if you compare the Western Ring Route to the cost of a three-lane version of the Clark government proposal there is almost a $700m difference between the two.

That's not a difference of $1b, but in the context of this election what's a few hundred million?