Kopu Bridge
The Kopu Bridge (originally Hauraki Bridge and sometimes Waihou River Bridge) is a single- lane swing bridge that spans the Waihou River, near its emergence into the Firth of Thames in the Thames-Coromandel District of New Zealand's North Island. The bridge was completed in 1928 and is part of State Highway 25. The swinging span in the middle of the bridge is 43 metres long and with an overall length of 463 metres, the bridge is the longest and oldest single lane bridge within the state highway network. As the first available crossing of the Waihou River and the main link between the Hauraki Plains and Coromandel Peninsula, it sees a lot of traffic, especially during holidays. Due to a gradual increase in the traffic between Auckland and the Coromandel Peninsula, by the early 1990s the bridge became the most heavily used single lane bridge in the country, with traffic volumes of an average of 9,000 vehicles per day. Traffic flow over the bridge is controlled by traffic lights and the bridge is notorious for queues which form during peak times such as holiday weekends, when three hours delay are common. As of 2010, construction on a replacement bridge is ongoing directly to the south of the old Kopu Bridge. While rarely used nowadays as boat traffic has declined (especially for shipping use, with the river once navigable all the way up to the town of Paeroa), the swing span can still open, and provide a 15.3 m wide channel to passing vessels. The bridge is the only surviving road bridge of the swing span type in the country and the New Zealand Historic Places Trust lists the bridge as a Category 1 historic place, while it is also on the IPENZ Engineering Heritage Register.

The original bridge was built in 1928, under the lead of the Main Highways Board after negotiations over its construction started in 1911, and planning begun in 1922. It was one of the largest such works of its time, with 23 spans and advanced deep piling for the soft ground of the river bed. It replaced the barges and ferries which had until then served to cross the Waihou River, connected Thames to the newly drained dairy farming grounds of the Hauraki Plains, and was reckoned to have made a big difference to the local district, having marked the local shift from river transport to road transport becoming dominant, and to Thames moving from a mining town towards a farming service community. It was also considered a project typical of the time and of New Zealand Prime Minister Gordon Coates quest to develop the rural economy. Up to the 1960s, traffic used the passing bays, but after angry confrontations between motorists had become more common, lights were installed. Until that time, the bridge had still sometimes used for herding of livestock, but soon after the signalisation, further increasing traffic queues began causing calls for a replacement bridge. In late 2009, a webcam was installed to allow online checking of queue lengths during the holiday periods, a feature that in New Zealand had so far been limited to urban areas.

In addition to the constrained traffic over the bridge (with flows projected to increase by 2% per year over the next 15 years), investigations in 2001 had also found that the bridge was likely to be severely damaged or might even collapse in an earthquake stronger than that of a 300-500 year return period, and that it had failed to pass safety inspections which require the ability to withstand a 2,500 year return period quake. In 2006, Transit New Zealand announced their intention to build a second bridge slightly upstream of the existing bridge and to route the State Highway over the new bridge. However, the start date was at that time set for no earlier than 2011, which was later brought forward to late 2009 by National as part of an economic stimulus package. The new bridge will be 587 m long, and have 16 spans, with its foundations being driven 36 m to 50 m deep into the riverbed, due to the soft swampy ground not providing good support otherwise. Much of the ground would also have to be forcibly compacted first. The design incorporates images of waka and taniwha, and landscaping using native plants. The replacement was to originally cost $32 million, this later rose to $47”“48 million, also including 2.5 km of new approach road as well as a new roundabout near Thames, The bridge's navigation channel at the central span will be 42.8 m wide and 6.5 m above mean sea level, allowing larger vessels to pass under it, without the need for a swing bridge as for the old structure. As of February 2010, works on the new bridge were reported as proceeding on schedule for a 2012 completion, and employing around 40 people on site, and another 100 in the wider area, with NZTA making an effort to source much of their material locally. The New Zealand Labour Party has however criticised this claim, noting that only 3,000 of the 11,000 tonnes of steel to be used are sourced from within New Zealand, despite claims that the country's steel industry was well able to provide the remaining steel in terms of volume and quality. As of January 2011, 10 of the 15 piles for the new bridge had been sunk. However, the contractor noted that this would not enable an earlier-than-expected completion date - since it would still take more time until the soft soils on the approach roads was sufficiently compacted and stable under a bed of rubble (though 1 m settlement had been reached as of early 2011, 2m will be required). Therefore, the expectation was still for completion in mid 2012. Due to its historical significance, the existing bridge will be retained and upgraded, possibly to be integrated into a new cycleway along the coast - though the new bridge will also provide access to cyclists and walkers.