The Waterview Connection appears to be doing what it was designed to do, with Auckland commuters reporting free-flowing motorways on Monday morning.
The New Zealand Transport Agency will be breathing a sigh of relief, after Sunday's gridlock through the $1.4 billion tunnel, which connects the Western and Southwestern motorways.
"We do a lot of modelling before we opened the tunnel and so we had some idea of how it was going to operate, but you're never 100 percent certain," NZTA spokesman Brett Gliddon told Newshub.
They had "way more [traffic] than you'd expect on a normal Sunday" trying to get through the tunnel, which opened around midnight that morning.
"It's gonna take a wee while for it to settle down, and it will take a few more morning peaks for us to get a real feel for how it's going to operate - but we were really pleased," said Mr Gliddon.
And so were Aucklanders, who took to social media to praise the new route through the city.
"Pleased to report that the Waterview tunnel has taken 10 mins off my drive time dropping Rocky off to school even tho it's raining today!" Twitter user @PeninaJoy wrote.
"#WaterviewTunnel flowing freely both ways. Wondering where the traffic is at tbh," said TV host and media commentator Russell Brown.
"Waterview Tunnel is great. Saved me 10+ mins this morning. Expecting a bigger number tonight!" added @shevy01.
Users on their way to the airport, one of the Waterview Connection's big selling points, also reported success.
"Took the Waterview tunnel this morning to airport from west Auckland. Reduced my trip length by over 10 minutes," wrote @NeyoTalks.
"Saved 10 mins travel time to the airport this morn thanks to the 2.4 km Waterview tunnel #govtkeepingAkmoving," tweeted Conservation Minister Maggie Barry.
NZTA says motorists choosing the tunnel freed up space on State Highways 16 (from the city's west to the CBD) and 20 (from Mt Albert to Manurewa).
It won't be clear until at least tomorrow whether today's free-flow was the result of motorists fearing tunnel tourists avoiding the area.
"It has probably operated better than we thought," said Mr Gliddon.
"We thought we might have had a bit more traffic going through it, but we weren't sure because it's only the second day - people are still going to have a look at it, as well as people using it for general reasons."
There have been no reported incidents or crashes.
"Behaviour in the tunnel has been really good. There's no lane-changing going on and everyone's driving to the 80km/h speed limit so we thank road users for that because it does make it all run a lot smoother."
The AM Show sent a reporter to the tunnel on Monday morning, and even though it was peak traffic, she was able to drive the length of the Waterview Connection 20 times while the show was on-air.
Photos from NZTA just after 11am at both ends of the tunnel showed empty roads.
"It's really good to see the opening of the Waterview Tunnels have gone smoothly with 78,000 vehicles using them on its first day of being open," Transport Minister Simon Bridges told Newshub.
"The new connection will transform the way people and freight move around Auckland. It will take time for new traffic patterns to settle but will ultimately provide a more resilient transport network for Auckland."
On Sunday, he said in a statement the "improved productivity and reduced travel time" would add $430 million to the New Zealand economy.
He also said the city's cyclists would also benefit, with the expansion of the cycling and walking shared path alongside the motorway between the southern end of the tunnel and the Maioro St interchange.
"This has been a long awaited and eagerly anticipated piece of transport infrastructure envisioned decades ago. It's fantastic that New Zealand's biggest and most ambitious transport infrastructure project is now open to vehicles."
Scepticism despite early success
With NZTA admitting it will be a while before the full impact of the tunnel will be known, some believe it's destined to only add more congestion.
"It will be a very useful piece of infrastructure off-peak, but on-peak they fall to the logic of all urban highways everywhere in cities, which is that they induce more driving, therefore they induce traffic congestion," said Greater Auckland traffic expert Patrick Reynolds.
Others on social media said the traffic benefits would have been greater had that $1.4 billion had been spent on rail and buses.