From bespoke to blueprint: tackling Aotearoa New Zealand’s bridge-building challenge

New Zealand faces its biggest bridge rebuild in history, and WSP is driving innovation through standardisation and modern construction methods to deliver faster, greener, cost-effective solutions.

Jeremy Waldin

Head of Bridges, Maritime & Structures

New Zealand

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Over the coming decades, Aotearoa will embark on one of its largest-ever programmes of bridge rebuilds. It will be an ambitious national effort to replace hundreds of ageing structures, many of which were constructed in the first half of the 20th century.

The scale of the task ahead is gargantuan, riddled with engineering, environmental, and logistical complexities. Yet history has shown the key to success lies in smart design standardisation as well as the adoption of modern methods of construction (MMC) - approaches that promise to make the process faster, more efficient, and easier on the public purse.

WSP is already setting a benchmark in this space. Projects like the Homer Tunnel show how innovation and standardisation can deliver faster, more efficient outcomes. Recent bridge replacement projects have also demonstrated that, with the right planning and technology, even the most challenging rebuilds can be completed with minimal disruption and maximum efficiency.

In doing so, it’s useful to look back through history. Jeremy Waldin, WSP's Head of Bridges, Maritime and Structures, says the first large wave of bridge building in New Zealand happened in the mid-19th century.

“These first-generation bridges were typically constructed from timber, wrought iron or cast iron and often constructed using techniques imported from the UK and Europe. The majority of these structures were replaced throughout the 20th century typically due to durability issues, capacity constraints or damage in major flood events”.

A further wave of bridge construction emerged in the 1950s and 60s, spurred by a doubling of car ownership in New Zealand. This era saw the rise of steel, steel-composite, and pre-stressed concrete bridges. But it’s the second-generation stock of reinforced concrete bridges that now demands the most urgent attention.

“We’re now facing one of the largest waves of bridge replacements in our history,” says Jeremy. “Unlike the replacement of first-generation timber, wrought and cast-iron bridges, which occurred gradually as these bridges failed or were washed away, this time we’re dealing with a large number of second-generation bridges all ageing out at once.”

The numbers are staggering. There are over 4,600 bridges and large culverts on the state highway network, over 1,500 on the rail network, over 10,000 managed by local councils, and over 10,000 footbridges, boardwalks and structures owned and managed by the Department of Conservation.

The second generation of bridges within New Zealand were typically built from reinforced concrete, steel or prestressed concrete. A major construction boom occurred between the late 1920’s and mid 1940’s, when over 20% of all the current road bridges in New Zealand were built. These were predominantly reinforced concrete, which was a cutting-edge material at the time. Many of these bridges are still standing today, but Jeremy says their time is running out.

“Reinforced concrete carbonates over time. In coastal areas, chloride ion ingress can also accelerate deterioration. Many of these bridges are now approaching 100 years of age and are starting to show signs that they are near their end-of-life.”

When you add them all up, we have more bridges per capita than almost every other nation in the world, we’re a nation of bridges.

Jeremy Waldin Head of Bridges, Maritime and Structures, WSP New Zealand

Jeremy Waldin Head of Bridges, Maritime and Structures, WSP New Zealand

In tackling this monumental task, part of the answer lies in embracing modern methods of construction and, crucially, standardisation.

Jeremy says the only way we can do this economically is to get smarter. That means building efficiently, quickly, and with minimal disruption. Speed, he says, isn't just about cost. Quick construction limits environmental impact, reduces disruption to the public, and allows infrastructure decisionmakers to respond more effectively to natural disasters like Cyclone Gabrielle and the Canterbury and North Canterbury Earthquakes.

Standardisation will play a pivotal role. By developing a suite of interchangeable components - including standardised superstructures, pier caps, piers, columns and pile sizes - engineers can create a ‘building block’ approach to bridge construction. This not only streamlines the build process but also enables stockpiling of critical components for rapid deployment in emergencies.

Jeremy points to the Homer Tunnel project as a case in point.

“That project was all about innovation. We designed precast elements, shallow foundations, and used 3D modelling to create a complex structure that slotted together seamlessly. It was all about speed and precision to construct a structure within a tight avalache off-peak season.”

Lessons from Homer Tunnel and elsewhere are now being applied to bridge replacements across the country, where WSP is investigating options for pre-cast pier-cap details and connections.
However, standardisation isn't without its challenges. The country’s highly variable ground, river, and seismic conditions mean that a one-size-fits-all approach is not feasible.

“At the moment, almost every bridge looks different,” says Jeremy. “But we can still standardise intelligently - by creating a range of components tailored to different conditions.”

He says that collaboration is key - including working closely with contractors and fabricators to understand how they build, and design solutions that are efficient to construct at scale.

Early procurement is also critical. As a small importing nation, New Zealand faces long lead times for materials like steel. If bridge designs can be based on standard measurements, this improves the ability to order in bulk and avoid delays.

There are already promising signs. KiwiRail has developed standardised superstructures for its network, and New Zealand has a long history of standard designs for road bridges - dating back to the Ministry of Works era.

“In the late 1920’s and 1930s, Aotearoa built bridges at an incredibly fast rate, using standardised designs and state-of-the-art materials” says Jeremy. “In 1939 alone, the Ministry of Works opened over 7,600m of new bridging which was a phenomenal feat, especially given the manual construction techniques at the time. Their designs included standard beams, superstructures, barriers, piers and piles. We need to learn from that history and drive it forward, constructing New Zealand’s third-generation of bridges using modern methods of construction and advanced materials such as FRP, low carbon concrete and low carbon steel.”

Today, various consultants and clients produce a range of bespoke bridge designs. While this creates challenges, standardisation and more efficiency can still be created by applying the lessons of the past using modern tools and methods. Doing so will mean a trade-off. Bespoke designs can be optimised to reduce material use, which is generally better for sustainability. But Jeremy says standardisation offers its own environmental benefits.

“When you build fast, you reduce disruption to the public, time in waterways, and machinery use, helping to lower carbon emissions and save time and money. It’s about finding the right balance - using standardised components intelligently to achieve both speed and sustainability.”

As New Zealand prepares for this upcoming wave of bridge replacements, the path forward is clear. By embracing innovation, standardisation, modern methods of construction, state-of-the-art materials and collaboration, we can ensure that the next generation of bridges is built not only to last - but to lead.