The $1.4 billion Waterview tunnel will open to cars around the first weekend of July - but an exact date is not being given for safety reasons and to avoid queues of motorists.
The "soft" opening was announced at today's formal opening by Prime Minister Bill English and Transport Minister Simon Bridges, who cut a ribbon to mark the completion of the longest road tunnel in New Zealand.
It completes the 48km western motorway ring route - a second motorway route through Auckland - and includes a giant motorway interchange at Great North Road to connect the Southwestern and Northwestern motorways.
This latest connection in Auckland's state highway network will provide a more resilient and reliable motorway network by reducing the current dependence on State Highway 1 and the Auckland Harbour Bridge
Thousands have turned out for the opening and will get to walk and cycle through the twin 2.4km long tunnels under Waterview once the formalities are finished about midday.
Bridges described today's celebration as the biggest change in Auckland's transport system since the opening of the Auckland Harbour Bridge in 1959.
On that occasion, 106,000 Aucklanders walked over the bridge before it was opened by the Governor-General Lord Cobham on May 30, 1959.
At five opens days over the next 10 days, 60,500 people will have a once in a lifetime opportunity to walk and cycle inside the tunnel, with its 140,000sq m of paint - black for the roof, white for the walls - 4000 lights and 400km of cabling and wiring.
Each of Waterview's tunnels was bored by a giant tunnelling machine, named Alice. At 2.4km long, Waterview takes the record off the 1.97km Lyttelton tunnel as the longest road tunnel in New Zealand.
"The Waterview Tunnel is one of the most important infrastructure developments to take place in New Zealand and will help unlock Auckland's potential as a world class city and secure its future economic prosperity," Bridges said.
The western ring route - linking the west of Auckland, Manukau, the city and the North Shore - is one of the Government's Roads of National Significance and was prioritised because of the contribution it will make to our fastest growing city, the transport minister said.
"It will provide more options to Aucklanders travelling around the city, more efficient links to and from Auckland Airport, Ports of Auckland and inland freight hubs, reducing costs for people and businesses, not only in Auckland, but throughout the country," he said.
Wider economic benefits are estimated to be worth $430 million, through improved productivity and reduced travel time, and also include the creation of more than 18,000 jobs.
"This latest connection in Auckland's state highway network will provide a more resilient and reliable motorway network by reducing the current dependence on State Highway 1 and the Auckland Harbour Bridge," Bridges said.
"New bus shoulder lanes will mean more efficient journeys for people using buses to travel to and from the central business district and demonstrate the Government's commitment to better public transport.
"Significant upgrades and an extension to the Northwestern Cycleway will provide a safe, separated and enjoyable route for pedestrians and cyclists, between the city and western suburbs.
"This has been a long awaited and eagerly anticipated piece of transport infrastructure envisioned decades ago. I'm thrilled to be opening New Zealand's biggest and most ambitious transport infrastructure project which will help transform Auckland's transport and economic future," Mr Bridges says.
The $1.4bn Waterview Connection is New Zealand's largest ever roading project. It includes construction of twin 3-lane tunnels - they are the longest road tunnels in the country - and a giant motorway-to-motorway interchange at Great North Road to connect the Northwestern and Southwestern Motorways, improve network resilience and travel time reliability.
The Waterview Connection will provide a second route through Auckland, bypassing the city centre, creating greater reliability and resilience. While it's not designed to remove congestion altogether, the western ring route will provide a better balance of traffic flows across the entire road network, including helping to remove cars from local roads.
As well as helping to cater for future traffic demands, it will also provide more transport options including bus lanes and walking and cycling connections.
WATERVIEW TUNNEL FACTS
Each of Waterview's two tunnels is 2.4km long - twice the length of the Auckland Harbour Bridge.
They will each carry 3 lanes of traffic.
The tunnels are the longest road tunnels in New Zealand - the Lyttelton road tunnel at 1.97m previously held the record.
Tunnelling first began at Waterview in 2013. The first tunnel was completed in 2014. Alice the Tunnel Boring Machine broke through on the second tunnel on 19 October 2015.
The Tunnel Boring Machine was specifically designed for the Waterview geology by the German company, Herrenkencht, and manufactured in China.
The Tunnel Boring Machine was 87m long.
At construction peak up to 1000 people worked on the project.
The fit-out programme included:
· Compacting 74,500m3 of aggregate for backfill
· Laying almost 5kms of drainage pipes
· Installing 104 flame traps.
· 140,000m2 of paint is being applied - black for the roof, white for the walls
· 4,000 lights
· 62 ventilation fans
· 50kms of cable trays to support wiring and other equipment
· 400kms of cabling and wiring
· CCTV cameras and signage is also being installed
· 5 deluge storage tanks each containing 250m3 of water for fire control. Each deluge set will supply 10mm of water per minute inside each of the 173 zones of the tunnel. Each zone is located every 30m in the tunnels.
The Waterview Connection project is being delivered by the Well-Connected Alliance which includes the Transport Agency, Fletcher Construction, McConnell Dowell, WSP, Beca Infrastructure, Tonkin & Taylor and Japanese construction company Obayashi Corporation. Sub-alliance partners are Auckland-based Wilson Tunnelling and Spanish tunnel controls specialists SICE.