KEY POINTS:
Relief in the shape of a new motorway is at hand for drivers sick of inching along a two-lane ridge road to get between Auckland's western and northern quadrants.
Largely hidden by bush from bumper-to-bumper traffic along Upper Harbour Drive, once a quiet country road, road-builders have been
toiling for four years on a 5.5km motorway through Greenhithe's gullies and hills to Albany.
Their efforts will bear fruit for motorists tomorrow, when the new $110 million link and a duplicate bridge built across the upper Waitemata Harbour for $37 million will open for traffic.
Prime Minister Helen Clark will open the motorway this morning, after Maori blessings at dawn, but the local community will then be given an opportunity to inspect it before traffic gets to use it.
The motorway and bridge are the first additions to Auckland's western ring route since the Puhinui interchange opened on the Southwestern Motorway four years ago, although other projects are advancing through Mt Roskill and Manukau.
Work is expected to start in April on a 4.4km motorway link through Hobsonville and a 2.2km northern extension of State Highway 16 to Brigham Creek Rd for $240 million, a combined project due for completion in 2012 and deemed crucial to plans for a $1.2 billion town centre at Westgate tipped to create almost 9000 jobs.
Transit NZ expects the Greenhithe motorway to chop the typical morning peak travel time for commuters between the duplicate harbour bridge and Paul Matthews Rd in Albany's industrial estate by 80 per cent - from 25 minutes to five.
Motorway interchanges will end the need for Greenhithe residents, whose ranks are being boosted by large housing developments, to queue to join solid lines of traffic heading to work from Waitakere City.
Life-long resident and local community board member Malcolm Black said a five-minute trip to Albany at 6.30am often became a 30-minute exercise in frustration if left until 7.15am.
Site engineer Paul Clark of consultants Opus International said the motorway would have a 100km/h speed limit compared with the maximum 70km/h on Upper Harbour Drive.
He said commuters often prevented by heavy traffic from getting anywhere near that limit would be able from tomorrow to "put their foot on it".
Although the Herald has received messages from readers claiming the motorway could have been available for traffic well before Helen Clark's appearance, Transit insists there has been plenty of last-minute work to finish.
Its contractors completed the new three-lane bridge more than a year ago, but then had to close the existing 1975-built crossing for remedial work to reduce sagging from concrete shrinkage around its piers.
Traffic was able to cross the new bridge in both directions during the closure, but drivers will have their first chance tomorrow to use it as part of a duplicate motorway set.
It will be available to eastbound traffic only, with a fenced-off cycling and pedestrian path on its northern edge, leaving the old bridge for the exclusive use of motorists heading west. Although most of the motorway has two lanes and a shoulder in each direction, for potential bus priority travel, the new bridge has an extra uphill "crawler" lane.
The motorway passes under new bridges at interchanges with three local roads, two of them at Greenhithe and the other at Albany Highway, where about two-thirds of eastbound traffic is expected to peel off.
It will feed the remaining traffic into the eastern sector of Upper Harbour Highway, which Transit will consider eventually upgrading to a motorway connection with State Highway 1.
Transit project manager Rachel Kirk says that depends on being able to remove signals at its intersection with Paul Matthews Rd, which will require a bridge to minimise disruption to local traffic.
The new motorway's designers faced a challenge squeezing it and features such as two large stormwater ponds within a narrow corridor, under resource consent conditions to minimise the destruction of bush.
"We didn't have acres of land to play with," said Mr Clark, who also oversaw the laying of culverts for 16 streams to flow under the motorway to Lucas Creek in Waitemata Harbour's sensitive upper reaches.
To supplement the permanent stormwater ponds, in which islands have been built for ducks to roost, silt traps have been installed around all the streams.
Iwi representatives were involved in weekly inspections during construction to ensure water quality was not degraded.
About a million tonnes of fill for motorway embankments were taken from cuts through the hills, and bunds and noisewalls erected to minimise the impact on nearby housing of heavy traffic volumes.
Those volumes are expected to grow to 35,000 vehicles a day by 2011, compared with 24,500 now using Upper Harbour Bridge.