The Waterview Tunnel captured the public's imagination even before it was finished. Aucklanders followed the progress of Alice the giant boring machine with great interest and turned out in their thousands to walk and cycle through the $1.4 billion project when it was complete. On opening day the underground motorway was packed with excited motorists making a special Sunday afternoon trip to drive through the city's newest tourist attraction - then turning around at the southern end so they could drive through it again. The Waterview connection even made a cameo appearance in an election leaders debate, with National leader Bill English telling Labour's Jacinda Ardern he'd take his tunnel over her vision any day.

Now we know officially what all the fuss was about.

As many commuters have already discovered since opening day on July 2, the tunnel has made driving times shorter and more predictable around the city.

NZTA figures show it took an average 24 minutes to make an afternoon trip from the CBD to the airport using the new tunnel from July to September and 25 minutes to get from the airport to the city centre.

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The average pre-tunnel travelling time using the old Manukau Rd-Gillies Ave route in June was 24-32 minutes to the airport and 35-44 minutes to the CBD. The old route now takes an average 27 minutes and 33 minutes respectively, slower than the tunnel but still more consistent than it used to be.

As NZTA points out, predictable travel times - on the airport route in particular - are hugely important to businesses, which rely on timely deliveries. Travellers looking to time their airport run will also appreciate the improvement.

Even more importantly, the tunnel has taken the pressure off State Highway 1 and the surrounding road network by linking the northwestern (SH16) and southwestern (SH20) motorways to create an alternative route through the city. A trip into the CBD from Papakura on a weekday now takes 49 minutes on average, compared to 46-70 minutes before the tunnel opened.

Travel times are down 7 per cent on SH1, as some drivers switch to the alternative route. NZTA says travel times have also become more consistent on major local roads such as Sandringham Rd, New North Rd and Dominion Rd.

There is more work to be done. Southbound morning commuters still suffer long queues as they join SH20 at Maioro Rd by the southern tunnel exit, suggesting the new route has not displaced as much through traffic from local roads as planners had hoped.

And rush hour traffic still slows to a crawl when SH20 shrinks from three lanes to two at Hillsborough, undermining the whole purpose of a free-flowing motorway circuit.

The project has also attracted criticism for the 80km/h speed limit imposed not just in the tunnel itself but on the surrounding motorway as far north as Western Springs.

The lower speed limit collected $948,220 in fines in six weeks but a petition has persuaded NZTA to restore the limit to 100km/h on the motorway, which seems fair.

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Overall the Waterview tunnel has been a great success. It is a reminder that solving Auckland's transport problems will take concerted action on several fronts.

The city desperately needs a better public transport system but improvements to its creaking road infrastructure are also long overdue.