Is the $1.4 billion Waterview Tunnel opening this weekend?
The Weekend Herald understands it will open unannounced this weekend - but NZTA is not confirming details for safety reasons.
Thousands have already walked through the tunnel, and earlier this month NZTA said it expected the tunnel to open to traffic "around the first weekend of July".
But it said it would not give the date or time to avoid queues of motorists.
NZTA is expected to open the 2.4km tunnel at a quiet time on the road, meaning it may be late at night or early in the morning. It is understood the authority wants to test its safety barriers and other procedures during the initial opening phase.
"Because it's such an impressive piece of transport infrastructure we expect many people will want to drive through the tunnel to see it first hand and therefore heavy traffic and queues are likely," NZTA said in a statement tonight.
When new highway infrastructure opened in the past, such as the Northern Gateway Toll Road, there were long queues of people waiting on the side of the motorway which became a safety issue, NZTA said.
"To reduce the likelihood of this occurring we will not be announcing the exact opening time."
The public is being encouraged to plan their journeys and expect it to take some weeks after the opening, for traffic flows to adjust.
The tunnel completes the 48km western motorway ring route - a second motorway route through Auckland - and includes a giant motorway interchange at Great North Rd to connect the Southwestern and Northwestern motorways. The route is alternative to Auckland's State Highway 1, linking Manukau, Auckland, Waitakere and the North Shore,
The opening was delayed in March, due to continuing testing and commissioning of complex systems to ensure the safe operation of the tunnel.
It was initially expected to open in April this year.