Mangere Bridge, officially also called the Manukau Harbour Crossing, is a motorway bridge over the Manukau Harbour in south-western Auckland, New Zealand, crossing between the suburb also known as Mangere Bridge (southern side) and the suburb of Onehunga (northern side). Completed in 1983, the current bridge carries a four-lane motorway (carrying approximately 80,000 vehicles daily)[1] with a cycle and pedestrian path also suspended underneath the western side of the bridge.
In April 2008, work began on a duplication of the bridge to cater for increased traffic (completed in 2010),[1] and to serve up to 160,000 vehicles per day in 2021).[2] The process was being delayed by disagreements over design and funding, as well as over the scope of the bridge project and an associated interchange - with the interchange being scaled down after concerns from the local community.
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The initial bridge in this location was built of timber and opened in January 1875. Rather narrow, it also soon began to be attacked by shipworms, and in 1910, more than 30 of the piles had been replaced, as well as the decking.[3] The bridge was also single-lane, and so narrow, even pedestrians could barely pass a vehicle safely.[1] The bridge was eventually considered structurally unsound and closed in 1914,[1] before being fully demolished.
In January 1914 (according to some sources, only in 1915),[1] a 246 m long replacement bridge was opened instead. Designed by R.F. Moore, the designer of Grafton Bridge, it was also built by the same company, the Ferro-Concrete Company of Australasia (in a time when almost all bridges in the country were being built by the Public Works Department). The ferro-concrete bridge with driven concrete piles was considered a substantial engineering achievement in its time. With a width of 11.6m, it allowed for a double tram track. The bridge however did not provide for enough clearance to let anything but small boats pass under it.[3] In World War II, an anti-tank road block was erected on the bridge near the middle of the spans, with a small sentry shelter close by. The structure has since been removed, and it is unclear whether the bridge had also been mined.[3]
However, the new bridge also soon proved to have too little capacity, and sinking foundation piles created issues.[1] The old bridge was closed in the 1970s to motor vehicles[4] and is slowly deteriorating as of today, especially after it sustained damage when a ship accidentally rammed it some years ago. A second ship, the 300 ft container transport Spirit of Resolution, also crashed into the old bridge on 8 October 2005 as it attempted to leave a nearby Port of Onehunga berth during winds estimated later on as being between 30-40 knots (with stronger gusts) and against a strong incoming tide. The collision occurred despite the ship's bow thrusters working at full power and a small harbour tug assisting.[5]
As problems with the quality of the aging concrete and steel also make it unlikely that the 'Old Mangere Bridge' can be retained permanently,[3] it was envisioned that the bridge would be dismantled and replaced by a newly designed footbridge. However, complaints about this course have for now (2006) stopped these plans while 'heritage options' are being considered as part of the general transport plans in the area.[4] As of 2008, it is intended to retain the old bridge as a cycling / pedestrian link, and maintenance funds have been set aside for this continuing use.
The current (as of 2009) Mangere Bridge was opened for traffic in 1983, and now carries approximately 80,000 vehicles a day.[1] The motorway bridge had taken 8 years to build, due to labor and redundancy pay disputes which among other delays caused a stop to the work for 2 years.[6]
Due to the limited capacity of the bridge, a duplication of the structure was decided on and eventually completed in 2010.
On 17 May 2006 Finance Minister Michael Cullen announced in the Budget that funds were being allocated to Land Transport New Zealand, to help the National Land Transport Programme accelerate certain projects. This includes funds for duplicating of the 1983 bridge to its east. The Programme indicated that only $2.78 million funding was then approved for investigation of the project, though Transit New Zealand might apply for additional $1.5 million for further investigation of this project in the current financial year. The bridge was at that time expected to cost NZ$330 million.[7][8]
As a wider part of the Manukau Harbour Crossing Project, the motorway is also to be widened between Walmsley Road in the south and Queenstown Road in the north from four lanes to six lanes. This widening will predominantly take place to the east of the existing motorway. The Onehunga interchange (known as the Gloucester Park Interchange) will be significantly reworked, to provide a more logical link with the motorway, and to ease congestion along Onehunga Harbour Drive. A standard diamond interchange was initially chosen by Transit, but after consultation with Auckland City Council this was then reworked into a quarter-diamond design, with the northbound onramp hooking underneath a proposed Neilson Road bridge.
As part of that investigation, Transit did consider whether it would have been worthwhile to toll new capacity to assist in funding its construction. This could have been in the form of tolling the new lanes along this route, which would ensure an untolled alternative is available (as legally required), while the tolled new lanes would be far less congested. In mid 2007, Transit indicated that it would not seek a decision on funding the bridge via road tolls before starting work on construction. Auckland Airport had accused Transit of threatening to defer the project if it could not gain backing from the public and local Councils. As the bridge is to be finished for the 2011 Rugby World Cup, further delays would possibly have resulted in the bridge not being completed in time.[7]
In early 2007 Transit indicated that it would be "more than willing" to develop a bridge that could also accommodate a rail link, intended for a possible future Auckland City - Auckland Airport rail link using the Onehunga Branch, (which reopened for passenger traffic on 18 September 2010). The railway currently terminates near the northern end of the bridge. A combination solution was debated which would see a rail link use the same bridge foundations. The change came after repeated lobbying by the Auckland Regional Council, which was of the opinion that a previous provision - restricted to allowing space for an additional, but separate bridge - was not sufficient.[9]
In September 2007, ARTA proposed to pledge NZ$ 2.5 million for future-proofing works which are to ensure that a rail link can be included in the future. The design envisages the future railway line run on the new bridge piers for part of the distance underneath the motorway structure, thus saving some of the high costs associated with strengthening the bridge to be able to take a cantilevered bridge - estimated at around NZ$ 20 million in extra costs.[10] The bridge is already intended to accommodate bus shoulder lanes.[11]
In July 2007, Auckland City Council commissioners gave approval to widening the approach motorway for the bridge through Onehunga Bay, but opposed the new interchange design north of the bridge as favoured by Transit, which intended to construct it around 7 m high over Gloucester Park and the Hopua volcanic tuff ring. A favoured version would instead be built in a cut and cover tunnel.[8]
The recommendation, which Transit could have ignored only at the risk of drawn-out legal fights at the Environment Court level (which would be likely to delay the project until after the 2011 Rugby World Cup), was based on the concerns of residents, who fear that the new interchange would increase and cement separation of their suburb from the Manukau Harbour.[8] Partly due to this, Transit New Zealand decided in August 2007 to continue with building the new bridge without including new interchange for the time being.[12]
The new bridge will provide four southbound lanes and bus shoulder lanes (as many lanes as the existing bridge, which will become reserved for northbound traffic). One of the lanes will be dedicated to local connectivity between Onehunga and the Mangere Bridge suburb only.[13] Transit New Zealand also confirmed that some provision will be made for a future rail link under both bridges to connect to Auckland Airport,[2] with three of the eight piers constructed strong enough to carry a future rail link.[14]
The bridge will have 7 piers with a total of 14 columns, and consist of approximately 10,000 cubic metres of reinforced concrete (with the rebar weighing approximately 1,000 tons). Some of the piles were driven 50m deep, to avoid issues with the softer top layers in the Manukau Harbour. The bridge itself consists of single-pour concrete columns and form traveller-constructed balanced cantilever decks.[1]
The related works also include a widening of approximately 4km of associated motorway to ensure the new bridge capacity can be utilised.[6] Existing pedestrian and cyclist links (on the old Mangere Bridge closed to motor vehicles) will be maintained and connected to a shared path along the Mangere Bridge waterfront reserve,[2] via a new walking/cycling bridge over Onehunga Harbour Road - to link Onehunga to the existing walking and cycling route to Mangere Bridge suburb (over the 1914 bridge) and to the Waikaraka Cycleway.[6]
Construction of the new bridge officially began on 9 April 2008, undertaken by the MHX Alliance, a combination of the NZTA, Beca Infrastructure, Fletcher Construction and Higgins Contractors.[1] The construction work will, after expected completion of the new bridge in late 2010, also include a temporary closure of the old bridge for refurbishment works, with all works to be completed in early 2011.[1] As of early 2009, total costs are expected to be NZ$ 230 million.[1]
The bridge was officially opened on 25 July 2010, seven months ahead of schedule. This brings the number of traffic lanes available over the harbour to 10, 2 of them bus shoulder lanes.[15]
A number of works related to environmental mitigation, post-project landscaping or improvement of non-motorway transport links are associated with the project (and either paid for or undertaken by NZTA). These include a 3.5m wide replacement foot/cycle bridge over Beachcroft Road, a new 3.5m wide foot/cycle bridge over Onehunga Harbour road at the Old Mangere Bridge, an upgraded underpass under the motorway connecting to Onehunga, as well as improved links to the walking and cycling paths along the harbour and motorway edges and improvements works on the Old Mangere Bridge causeway. After finishing work, NZTA will also reinstate their large construction staging site along the southern harbour front as an open space, "passive recreation" park with Pohutukawa.[16][17]