Related: Victoria Park Viaduct & Tunnel

Newmarket Viaduct Overview

The existing Newmarket Viaduct was completed in 1966 to link the Southern Motorway to the city, the Harbour Bridge and to Spaghetti Junction. Instead of traffic traveling on Great South Road and through Newmarket Village itself. It was the first bridge in New Zealand to use a prestressed continuous box-girder design (method for overcoming concrete's natural weakness in tension), Freyssinet (prestressed) concrete hinges at the base and used cantilever construction techniques.

The bridge opened in 1966 at four lanes wide (two in each direction) with space for six, the bridge was opened to full capacity (three lanes in each direction) in the 1970s in time with the construction of Central Motorway Junction (Spaghetti Junction).

Before the upgrade the bridge had come under criticism due to the fact that debris flies off the viaduct to busy Newmarket below, seismic susceptibility, that the bridge has been separating in sections to create wide gaps and limited stopping space.

In 2009 the Newmarket Viaduct carried 161,490 vehicles per day with the split being; southbound at 83,117 VPD and 78,373 VPD for northbound. More on State Highway Volumes in the Glossary.

In September 2010 the new southbound viaduct was completed and opened to traffic at three lanes wide, in May 2011 it was opened to four lanes wide. In September 2010 demolition of the existing southbound viaduct commenced along with the construction of the northbound viaduct.

Why did the viaduct need to be replaced?

Aged: The Newmarket Viaduct was beginning to show its age: non-compliance with earthquake standards (less than 1/200 year earthquake), poor quality barriers on the sides of the bridge, issues with storm water drainage, lack of ability to be widened and not enough safe stopping space.

Traffic Volume and the Spaghetti Junction Upgrade: Spaghetti Junction, following its recent upgrade, increased the volume of traffic it could handle, this pushed congestion to the Newmarket Viaduct. On the northern side of the viaduct there are four lanes in both directions and only three on the bridge (in both directions). Originally 83,117 had to enter three lanes from four in the southbound section, this caused significant congestion.

Ability to be upgraded: The Newmarket Viaduct did not have the ability to be upgraded (widened).

Newmarket Viaduct Replacement Project

Under construction since June 2009 | $215m | Completion: Late 2012 (total of 49 months). Full timeline.

The above graphic is an animated GIF and should play automatically through the five stages.

The Newmarket Viaduct Replacement is replacing the existing Newmarket Viaduct by constructing two new viaducts (one in each direction). The new southbound viaduct being east of the existing southbound viaduct and the new northbound viaduct in place of the existing southbound one. This equals the staged demolition of the existing viaduct and the new viaduct being around 20m east of the existing viaduct footprint.

The current stage is the demolition of the existing northbound viaduct. Once that is finished the project is complete. All traffic is now using the new viaduct.

Construction method

The new Newmarket Viaduct is constructed using a pre-cast segmental balanced cantilever method. This is basically a balanced cantilever method with each (girder) section built (cured, pre-stressed) off-site then installed onsite in a section by section basis.

A standard balanced cantilever method is where piers are constructed then girder sections are built on each side of the pier until they join to the other piers. They are constructed in unison from one central point outwards. This method was used on the Upper Harbour Motorway Greenhithe bridge construction and illustrated below:

With the Newmarket Viaduct replacement, a segmental balanced cantilever method does not require construction of the girders at site, the girders are constructed and pre-cast in East Tamaki (this allows for less disruption). The 'big blue' horizontal crane lowers each girder section on the ends of the bridge deck. Sections are still added in balance (unison from the middle/pier) until they meet other pier sections. This method does allow the crane to start at one end and finish at the other, without sections needing to be built from piers all at once.

A 'girder' is a box like pre-cast concrete structure, the top of the girder is the bridge deck and the hollow section underneath is where the strength lies. In this case the girders are built off-site and brought to Newmarket when ready to add to the structure. The overhead launching crane lowers the girder into position where it is glued (with an extremely strong epoxy) and fixed to the other girders (or pier girder) with tendons, cables and tongue & groove style keys. This is illustrated below:

Each girder weighs around 80 tonnes and all 498 of them are different and made to fit for the location intended.

Note: Certain girder may or may not contain the joint assistants mentioned above and all illustrations are provided as a indicative guide to illustrate the construction.

Images of completed sections

Above: Overview image of the new southbound viaduct when it first opened at three lanes in September 2010.

Above: Overview image of the new northbound viaduct which opened on the 29th of January 2012. The existing southbound
viaduct has been demolished and the existing northbound viaduct is in process of demolition.

Above: On the new northbound viaduct. The lanes will be made wider when the protection barriers are removed.

The Fourth Lane to Greenlane

Completed. Full timeline.

Part of the Newmarket Viaduct Replacement project is the continuation of the fourth lane from the new viaduct until the Greenlane interchange in the southbound direction. The reason to carry this extra lane is because 16% of traffic on the viaduct exits at Greenlane. The lane will terminate at Greenlane, and three lanes will continue south.

The map (left) shows where the lane extends from: Gillies Ave in the North to Greenlane in the South. The lane extends past the St Marks Road on-ramp and Market Road interchange and under the Omahu Road overbridge. Click Here for a larger version of the map.

This will require no land purchase or going beyond the original boundary.

Above: Widening and preparation of new alignment (from new southbound viaduct) next to the St Marks on-ramp.

Above: Construction continues to Greenlane. Taken from Omahu Road overbridge.

Project Timeline

The project is six months ahead of schedule.

Please note that the above timeline is matched from the NZTA timeline which they note is 'an indicative [timeline] and may be subject to change.'

Northbound Switch

The southern motorway was closed between Market Road off-ramp and the Gillies Ave on-ramp northbound between 8pm on Saturday the 28th to 3pm Sunday the 29th of January 2012 to allow for the new northbound viaduct to open. No long delays were experienced, this was attributed to Aucklanders avoiding the area.

Southbound Switch

The southern motorway was closed between Gillies Ave off-ramp and Greenlane off-ramp from 5pm on the 4th of September to 12pm Sunday the 5th of September 2010 to allow the southbound lanes to be transferred to the new viaduct and the blue gantry to be moved. This was completed ahead of schedule and reopened 17 hours before of the expected time.

Comments or questions?

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From: Martin | Instead of demolishing the last existing section of the viaduct in Stage 5 why can't this section be retained with reduced traffic load and maybe pedestrian access.

Answer: The existing Newmarket Viaduct is the least seismically stable structure on the Auckland Motorway network (mainly because of its construction techniques), so it is a risk if the viaduct remained. Also, I cannot see it being a viable pedestrian link as it is a motorway corridor that provides no access for pedestrians or cyclists (unlike a possible connection on the Harbour Bridge).

From: Karel | A great engineering feat. I use the St Marks on ramp daily and have found the work being carried out very interesting. The amount of delays experienced so far is really minimal. Well done and I hope it will be completed on time.

From: Harvey Weake | Absolutely brilliant! This is an incredible engineering challenge and once complete will put Auckland into a very strong position to maintain its world leadership status as a city to live in. We just need to figure out how to get separate cycleways installed across the inner city away from the mass transport system. Well done to the whole team driving this. You should feel very proud that your work is making a difference to all of us.