For the first time the impact the Waterview Tunnel has had on road travel in Auckland can be revealed - with the $1.4 billion project shaving up to 20 minutes off commuter traffic on the Southern Motorway into the CBD.
New data released to the Weekend Herald reveals the tunnel has been used for more than 6.6 million trips since it opened to the public on July 2.
And more than 400,000 vehicles are using it every week.
Its widespread use has led to some dramatic cuts on other in-demand routes in the Auckland transport network; including on the Southern Motorway, where a trip into the CBD from Papakura on a weekday is now taking on average just 49 minutes, down from up to 70 minutes before the tunnel opened.
Average time on traffic on suburban routes to and from the CBD have also been cut. And traffic times were also becoming more reliable and predictable.
"These travel time savings are great news not only for commuters but also for business productivity, because these improved travel times mean cost savings for hundreds of businesses," Brett Gliddon, the New Zealand Transport Agency's system design manager said.
"One of the Waterview Connection's key aims has been to provide a more efficient link between the port and airport to support growth and reduce the cost of doing business."
Gliddon said motorists were benefitting from "faster and more consistent and reliable travel times" since the tunnel opened.
The time savings were being provided by road users having the benefit now of a choice between travelling on SH1 and the Western Ring Route.
"That's helping rebalance the city's travel demands and is making both the motorway system and local roads more efficient," he said.
Travel on SH1 had dropped by around 7 per cent, with a growing number of motorists opting to now travel on SH20 and SH16.
"This redistribution is resulting in a more efficient motorway system with congestion relief equivalent to between 8500 and 10,000 fewer hours each day of total travel time on the motorways alone," Gliddon said.
"The redistribution of demand also allows the motorway system to more effectively absorb incidents such as breakdowns or crashes during busy periods."
Gliddon said the Waterview Connection - including its tunnels - was built to create extra motorway capacity and resilience.
A key aim was also to provide a second route through Auckland, bypassing the city centre, and resulting in a reduction on the reliance of the SH1 network and the Auckland Harbour Bridge, as well as freeing up local roads.
The stats showed that the tunnel was working, he said.
Non-motorway routes which were enjoying savings in transit time during week days - both to and from the CBD - included Sandringham Rd, New North Rd, Dominion Rd and Rosebank Rd.
A morning trip from Sandringham Rd to the CBD now took on average 8 minutes, as opposed to 7-13 minutes pre-tunnel.
From Great North Rd to the CBD in the morning is now taking 16 minutes, compared to 16-19 minutes pre-tunnel. The return trip in the afternoon/evening was takingg 15 minutes, as opposed to up to 20 minutes previously.
Traffic on Dominion Rd had also improved, with a morning trip inot the CBD now taking 10 minutes, compared to up to 17 minutes previously.
Barney Irvine - principal adviser, infrastructure, at the New Zealand Automobile Association, said its members were celebrating the benefits of the tunnel.
Feedback from AA members told of time saved across the board with people shaving anything from five to 30 minutes off their commutes.
"What people will have noticed is that the pressure's eased. They're getting to work and home at least a few minutes faster, and without as many unexpected delays," Irvine said.
"Even a saving of five minutes is gold. You're taking nearly an hour of pain out of people's lives each week, and letting them spend that time with their families instead."
"Projects like this - whether roads or transit - are never going to solve all of our congestion problems on their own, but they're vital if we're going to avoid being swamped by growth."
Earlier this week it was revealed nearly $1 million worth of speeding tickets were issued to Auckland motorists using the tunnel in just six weeks between July 21 and August 31.