Transport Minister Gerry Brownlee says a public private partnership (PPP) will be sought for the construction of the Transmission Gully motorway north of Wellington.
In June an independent board of inquiry approved resource consents for the billion-dollar roading project, which is planned to bypass the existing coastal highway north of the capital.
Mr Brownlee says the Cabinet has given approval to finance and build the highway using a PPP.
He says that decision will allow the Transport Agency to begin construction of the project in 2014 and open the road by 2020.
Mr Brownlee has also asked the agency to investigate the merits of charging tolls on the route in order to offset some of the construction costs.
But the Labour Party is calling on Mr Brownlee to release the business case for the decision to seek a public private partnership.
Labour's Transport spokesperson Phil Twyford says if the Government is so confident a PPP will cost less, it should put out to tender both the that version and a Crown-funded version.
He says that way the public can see the true cost comparison.