Transport Minister Simon Bridges is calling the opening of the Waterview tunnel, "the biggest change in Auckland's travel patterns since the opening of the Harbour Bridge in 1959". He may prove to be right.

The fact the NZ Transport Agency has scheduled no fewer than five days for people to walk through before it opens to traffic - the first opportunity is this Sunday - suggests a great many Aucklanders agree with him.

The same sense of history caused many to walk over the new bridge in 1959.

A tunnel is unlikely to attain the same status as a distinctive bridge on the landscape but it represents the completion at long last of the motorway network envisaged when the bridge was built.

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Once that final link in the chain opens for traffic next month, all the motorways should flow more freely.

The change in travel patterns should be most noticeable for airport traffic to and from the CBD, the North Shore and the northwest.

Rather than winding through the streets of Epsom, that traffic will be directed to the Northwestern Motorway.

The idea of travelling west towards Pt Chevalier when your destination is Mangere will seem strange at first.

But if that journey is as fast and smooth as planned, drivers will soon prefer it to a rat run though the central isthmus.

Unfortunately, it might not be quite as fast and smooth as planned. A few months ago the Transport Agency announced that entrances to the divided tunnel will have light controls.

Traffic leaving the Northwestern Motorway on ramps to the tunnels will be held up at busy times. It begins to sound like the tunnels may resemble the Harbour Bridge in more ways than the minister would like to admit.

The bridge, as Auckland well knows, was too small by the time it opened in 1959. Within a few years its capacity had to be doubled with "clip-on" lanes. If the Waterview connection soon needs to be widened, the solution will not be as simple.

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The wisdom of putting that stretch of motorway underground may be not be apparent if it becomes a chronic bottleneck.

But at least the $1.4 billion project is finished and must have ironed out whatever imperfections were found that caused the scheduled April opening to be delayed.

Infrastructure planners in this country have not be adept at anticipating population growth.

They either build too early - in the case of schools such as Long Bay College that waited an age for urban sprawl to reach it - or lag population growth, which was mostly the case with motorways.

Exceptions exist on the northwestern and southeastern edges of the Auckland where magnificent new motorways already await the city's projected spread.

They are the outer rims of a double circle of motorways - a figure eight in effect - that will be completed at Waterview.

The Transport Agency is warning that it will not remove congestion at a stroke, cities the size of Auckland can always expect congestion. But so long as road improvements keep pace, drivers will be grateful. Waterview is one to celebrate.