The Transport Agency has been given approval to ask private sector companies to put forward proposals to design, build and pay for a motorway north of Auckland.
The Puhoi to Warkworth road is the second road of national significance to be considered as a public-private partnership (PPP).
Transport Minister Simon Bridges said if private sector companies could not a offer a good deal the agency would resort to traditional methods of paying for the new road.
But he warned if a public private partnership did not proceed, work on building the new road would probably be delayed by about two years.
Mr Bridges said the first road of national significance to be considered as a public private partnership was Transmission Gully, north of Wellington, which is expected to open in 2020.
The Transport Agency hopes construction of the new section of state highway between Puhoi and Warkworth will begin late next year and be completed by 2022.
The existing motorway on State Highway 1 will have 18 kilometres of four-lane motorway added.
It is likely be built on the same basis as Transmission Gully, with a 25-year contract covering construction and maintenance.
The agency has previously estimated the construction cost at $760 million but the public private partnership (PPP) cost is likely to be higher as it includes maintenance and finance repayments.