A staged approach
An innovative staged approach will allow the NZTA to improve motorway capacity midway through the replacement project, and keep traffic moving in both directions throughout. This highly complex methodology will see construction taking place immediately next to the live motorway, therefore extra driver caution is required when travelling through this construction zone. Narrowed lanes and reduced speed limits are in place, so please, slow down over Newmarket (external link).
Stage 1, a new four-lane southbound bridge, was completed in February 2011. This includes a fourth lane to Greenlane, which was opened in May 2011 and helped to alleviate the traditional peak-hour bottleneck.
Stage 2 saw the southbound half of the existing viaduct dismantled to make way for Stage 3; the second half of the new bridge, which is due to be completed by the end of January 2012. Once Stage 4 has seen the removal of the last remaining traces of the old bridge (the old northbound lanes) mid way through 2012, the new bridge will stand alone, 13 metres to the north-east of where the existing bridge has stood for the last four decades.
- View staged construction/deconstruction sequence (PPT, 3.25MB)
Why replace the old viaduct?
With over 160,000 vehicles passing across it daily, the stretch of State Highway 1 between Gillies Ave and Greenlane represents a critical link in not just Auckland’s, but the nation’s roading network. At the heart of this link is the Newmarket Viaduct.
Constructed using groundbreaking engineering techniques and providing more lane space than was considered the norm for bridge structures at the time, the Viaduct was seen as a pioneering engineering development when completed in 1965. It was also, incidentally, the first bridge in New Zealand to be designed by computer. Forty years on however, the structure is showing its age, as it struggles to cope with the capacity demands of the 21st century - the need for modern engineering design apparent.
The demand for a wider main egress to Auckland’s south was formally recognised back in 2002, leading Transit New Zealand (the forerunner to the NZ Transport Agency) to commission a study into potential options for upgrading the Newmarket Viaduct. This decision to replace, rather than retrofit, took into account criteria such as environmental sustainability, construction impacts, timeframes, costs and likely benefits.
The new Newmarket Viaduct will be seismically strong enough to withstand a 1:2500 year earthquake, employ vastly superior noise attenuation measures and be robust enough to accommodate heavy vehicles currently embargoed from crossing over it. These significant improvements will remove a number of limitations associated with the flyover and create opportunities for more progressive development beneath and around it, beyond the traditional mix of parking lots and car dealerships.
| Key aim of project | Achievable with new structure | Achievable with retrofit |
|---|---|---|
| Add immediate 4th lane south | Y | Y |
| Preserve network capacity throughout | Y | N |
| Maximise seismic strength | Y | N |
| Enhance surrounding environment through urban design | Y | N |
| Markedly improved acoustic and edge-barrier performance | Y | N |
| Remove need for white chip surfacing | Y | N |
Note: Because temperature effects were not fully realised in the original design, the existing viaduct is subject to very high stresses resulting from temperature variations. The white chip surfacing that differentiates the road surface across the viaduct from the rest of the motorway is used to mitigate these stresses, however this material has become increasingly difficult and expensive to source. These stresses also act to reduce the useable life of the viaduct by constantly wearing away various structural elements.
Key benefits
Fourth southbound lane
A fourth southbound lane, which continues as far as Greenlane, has helped to ease peak hour bottlenecks exiting the city through a more graduated merging of traffic.
Improved seismic performance
The new structure is being built according to modern seismic standards to withstand a 1:2500 year event. Providing the main access route south of the city, the bridge is a vital piece of Auckland’s infrastructure, therefore its seismic capacity is a key component in the overall network’s integrity.
Stronger, safer …
Traffic patterns have changed markedly since the viaduct was completed in 1965 – even in the last 30 years the number of vehicles passing across the structure has more than trebled – putting extra pressure on the existing structure. This increase in volume has led to overweight vehicles being prohibited from driving across it. The new bridge will be able to accommodate all road vehicles, alleviating this extra pressure from the surrounding arterial routes.
Solid edge barriers, constructed to modern crash standards and incorporating elevated, slimline steel rails, will help to contain debris that would previously have fallen from the structure, improve noise mitigation and provide greater safety protection for drivers, while still preserving view shafts for passengers. Further safety, acoustic and maintenance benefits will be derived from a reduction in deck joints across the bridge.
… and smoother
The stretch of motorway across the new bridge will be surfaced with Open Graded Porous Asphalt (OGPA), which is noted for its skid resistance and noise attenuation qualities. This new surfacing will play a key role in minimising noise transfer to the surrounding area.
Urban design
The project’s scope does not simply detail a like-for-like bridge replacement, rather it explores the opportunity to enhance the land it spans and the surrounding environment. The existing structure has up to now prevented significant development beneath it. Through urban design and landscaping considerations, the new bridge has therefore been designed to connect more appropriately with the surrounding environment, and encourage investment to create a more community-friendly space around it.
Sustainability
From the provision for a fourth northbound lane across the viaduct, should future developments to the Central Motorway Junction allow for one, to the planting of flora chosen to encourage the return of birdlife to the area, the Newmarket Connection project has a long term vision.
Sustainability underpins the approach to the deconstruction process, as we have identified opportunities to recycle many components of the demolished viaduct. It is also envisaged that knowledge gained from this process will allow us to support our commitment to reducing carbon emissions through our wider portfolio of construction projects throughout New Zealand.
