Transport Minister Simon Bridges says Auckland's Waterview Tunnel will open to traffic in early July, calling it "the biggest change in travel patterns since the opening of the Auckland Harbour Bridge".
The New Zealand Transport Agency (NZTA) says the $1.4 billion Waterview Connection is New Zealand's biggest and most complex roading project, including twin 2.4km-long three-lane tunnels.
The opening of the tunnel marks the biggest milestone in the city's transport network in more than half a century, Mr Bridges says.
"Once open, it will transform the way people and freight move around Auckland.
"Together, the Waterview Tunnel and wider Western Ring Route will give more options to people and freight moving around and through Auckland, creating a more efficient, resilient and reliable network."
However NZTA Auckland highway manager Brett Gliddon told The AM Show in May the $1.4 billion tunnel will twice a day likely suffer the same gridlock as the rest of the city.
"We've never said it would fix peak congestion in the city," said Mr Gliddon. "There's still going to be a morning peak and an afternoon peak, and the tunnel will be a part of that."
Green Party co-leader James Shaw, responding to a Newshub tweet about the July opening, said the tunnel would be "completely congested" by August.
A ceremonial opening on Sunday, June 18 will be followed by public open day to allow people the chance to experience the tunnel up close before opening to traffic.
"The Waterview Connection is New Zealand's largest ever roading project and is a significant part of the strong investment the Government is putting into Auckland. This investment in the strategic motorway system will help support Auckland's increasing population and economic growth," Mr Bridges says.
"It largely completes the Western Ring Route, a new 48km route linking the west of Auckland, Manukau, the city and the North Shore."