The new northwest frontier

By ARNOLD PICKMERE

A new Auckland motorway link between North Shore and Waitakere is rapidly making its mark on the country surrounding the upper reaches of the Waitemata Harbour.

As State Highway 18, it will run westwards from the Northern Motorway via the present Upper Harbour Highway to where that ends at the Albany Highway.

At this point a new bridge, just started, will take the Albany route over the new motorway.

The new route will cut through Greenhithe to the Upper Harbour bridges and, a little later, along a new Hobsonville motorway section to join the Northwestern Motorway (SH16) near the Westgate shopping centre.

Q. What are the benefits?

A. * The present Upper Harbour Drive, a winding urban road along a ridge from the Albany Highway to the Upper Harbour Bridge, will become a minor route. At present traffic takes about 20 minutes to move through this area at peak times.

The rest of the existing 15km upper harbour route through Hobsonville and West Park goes through residential areas and is also prone to traffic delays.

* Once completed, the new route will have almost 12km of four-lane divided motorway, with provision for future bus priority lanes. * Transit's Auckland regional manager, Wayne McDonald, says that as well as linking North Shore and Waitakere cities and reducing congestion, it is expected to reduce reliance on the harbour bridge.

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Q. Will many people want to travel between east and west in that area?

A. Regional growth strategies predict substantial development in areas like Albany and Greenhithe in North Shore City, in Hobsonville and Redhills in Waitakere City and West Harbour and Kumeu South in Rodney District.

Some of this growth, both residential and commercial, is already occurring, especially in Albany and Greenhithe. Substantial traffic growth between North Shore and Waitakere is expected as a result.

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Q. What does the $250 million Upper Harbour Corridor Project involve?

A. * The Greenhithe Deviation, at $94.4 million, is about 5km long, following a route largely designated soon after the first Upper Harbour Bridge opened in 1975.

Work building a motorway through an area filled with ridges and involves a large earthmoving and drainage operation.

For example, raising the country to the planned road level in the Ashby Place area (near where the eastern end of the new deviation starts by the Albany Highway) will require 380,000cu m of fill.

Transit's Upper Harbour Motorway project manager, Bryce Carter, calculates that is enough to cover a rugby field to a height of about 55m.

It will be built up in layers only 200mm thick, each needing consolidation before the next is applied.

The project started last November. Estimated completion mid-2007.

* The Upper Harbour Bridge duplication, so called, is already being built. The $37 million balanced cantilever bridge will be 460m long, with a 60m conventional bridge and a widened 860m causeway reclamation leading to it at the western end.

A cantilever bridge is made of cantilevers projecting from the piers and connected by girders. The new bridge had been designed to blend with the existing bridge.

In fact, it is a better structure altogether, with three uphill traffic lanes including a slow lane. The existing bridge will be used for the two downhill motorway lanes.

The new bridge will also have a 3.5m wide pedestrian/cycleway lane protected by a concrete barrier.

At present, pedestrians and cyclists can use the existing bridge because it is state highway. When the new route is declared a motorway they will be prohibited.

They will use their special lane on the new bridge, then be diverted onto the existing local highway at either end, which should have less traffic than now.

The new bridge has twin piers (instead of single ones on the existing bridge) standing on piles drilled 12m into the sandstone under the harbour. It will also have a navigation span for boats, matching the one on the present bridge.

The new structure should be completed by mid-2006.

* The Hobsonville Deviation (5km), from the western end of the upper harbour bridges through Hobsonville to the Northwestern Motorway is a little further away, starting in the summer of 2005-06 and expected to take one to two years to build.

Planning for the interchange of the Upper Harbour Motorway and the Northwestern includes providing safe and easy access to the Westgate shopping centre, Hobsonville Rd and the West Harbour area.

At a date still to be finalised the Northwestern will also be extended by about 3km towards Kumeu ending at Brigham Creek Rd.