An independent board's draft approval of the proposed Transmission Gully inland highway linking Wellington with the Kapiti Coast is a significant milestone, the government says.

Acting Transport Minister Steven Joyce says the decision to approve the regulatory consents applications for the nearly $1 billion project is a very good step forward.

"This decision bodes well for this important project and the government is looking forward, as I'm sure the majority of residents in the Wellington region will be, to the release of the board's final decision in June."

New Zealand Transport Agency (NZTA) state highway manager Rod James says it will now study the decision and provide comments back to the Environmental Protection Authority (EPA), which administered the board of inquiry.

The government said in September it was fast-tracking the proposal which has been under discussion for decades.

The route is part of the Wellington Northern Corridor which runs from Levin to Wellington airport.

It is one of seven "roads of national significance" that the government has identified as essential state highways which require upgrading to reduce congestion, improve safety and support economic growth.