The Government is being accused of pork-barrel election bribes if it fast-forwards a second harbour crossing in Auckland without doing a proper economic analysis.

Auckland MP and Labour's transport spokesman Phil Twyford said he had been leaked information that Prime Minister John Key will make an announcement on the second crossing on August 12 - and it will be roads-only, with no rail option.

"It's a $5 billion project, a major piece of transport infrastructure. They're going to announce that they're going to bring it forward.

"It's currently on the books in the Auckland Plan to be built late in the 2020s. It has a 0.3 benefit-cost ratio (30c return for every dollar invested). So it's hard to see the numbers stacking up to build the second harbour crossing immediately. And there's a strong view in Auckland that it should include rail and roads."


Mr Twyford said his source did not know how far forward the Government wanted to bring the project.

He called it an election bribe.

"This Government has made an art-form of using transport projects as pork-barrel politics. We saw that recently, after starving the regions of transport projects for the last six years, they sprinkle $212m on regional New Zealand weeks before an election.

"It arguably is more of the same pork-barrel politics, if the decision is being made on a political whim without the benefit of proper economic analysis to determine its value for money. When they were elected six years ago, they hand-picked seven urban motorway projects and gave them the green light before they'd even done the economic analysis."

Transport Minister Gerry Brownlee, when questioned in the House, said the Government had no comment to make on supposed leaks.

Mr Twyford said the project should include rail.

"The Government recognises they are vulnerable on transport issues. Fixing the gridlock is the thing Aucklanders most want to see happen, and it's very clear from recent polling that Aucklanders want to see an emphasis on public transport.

"If my sources are correct and National is opting to build a roads-only second harbour crossing, I think that would be a real misjudgment by the Government. Aucklanders want their roads, but they also want a modern public transport system -- that second harbour crossing is an essential link to connect the northern suburbs with the city rail link and the rest of the regions' rail network.

"I note they are not supporting bringing the City Rail Link forward."

A spokeswoman for the Prime Minister said there were no imminent announcements about plans to accelerate the second harbour crossing.