Mangere Bridge (bridges)

Mangere Bridge, officially also called the Manukau Harbour Crossing, is a dual 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 older portion of the bridge carries a four-lane motorway (carrying approximately 80,000 vehicles daily) 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 1983 bridge to cater for increased traffic (completed in 2010), and to serve up to 160,000 vehicles per day in 2021. The process had been 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.

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. The bridge was also single-lane, and so narrow, even pedestrians could barely pass a vehicle safely. The bridge was eventually considered structurally unsound and closed in 1914, before being fully demolished.

In January 1914 (some sources, 1915), a 246 m long replacement bridge was opened. 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). This 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. 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. These structures were later removed, and it is unclear whether the bridge had also been mined.

However, the bridge soon proved to have too little capacity, and sinking foundation piles created issues. The bridge was closed in the 1970s to motor vehicles and is slowly deteriorating, 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 bridge on 8 October 2005 as it attempted to leave a nearby Port of Onehunga berth during winds estimated later 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.

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