What is a Bailey bridge?

A Bailey bridge is a prefabricated temporary single-lane bridge. They can be installed relatively quickly — anywhere from a few days to a few weeks depending on a range of factors. They provide an important temporary connection while the damaged bridge is repaired or rebuilt.

Developed by the British during the Second World War, Bailey bridges remain a cost-effective system, being versatile and relatively quick and easy to build and dismantle. With a basic component of a 3-metre-long truss panel, they can be configured to provide much longer spans.

The Bailey bridge ‘kit set’ systems are ideal for use in emergency situations (such as when bridges collapse or are washed out) and as temporary structures for planned events such as roading projects.

Bailey bridges have been used around the world for the past 80 years. Some of the most common uses in recent times in New Zealand have been:

  • replacing collapsed bridges
  • restoring access to roads washed out in storms (such as crossing a slip)
  • providing cost-effective temporary structures for roading projects
  • providing minor stream crossings for movie locations and other non-emergency situations.

How are Bailey bridges being used in the 2023 cyclone recovery in New Zealand?

Bailey bridges will be used as temporary replacement for some bridges lost or damaged during Cyclone Gabrielle and where a temporary bridge will help reconnect the community.

The National Emergency Management Agency (NEMA) currently has responsibility for prioritising the allocation of bridges in regions affected by Cyclone Gabrielle, with input from Waka Kotahi and local authorities.

Site preparation is undertaken by local authorities, and Waka Kotahi is responsible for bridge installation.

The following diagram outlines the process of damage assessment, prioritisation, site preparation and installation.

It’s important to understand that a Bailey bridge might not be the best solution for every bridge that has been washed away or collapsed. There are a range of temporary solutions available in New Zealand, or a river may be able to be forded instead. If the site conditions are difficult, a solution further upstream or downstream may be better suited. In some cases the best option may be to progress straight to a permanent solution, reinstating the bridge or culvert if resources permit.

How much Bailey bridge stock does New Zealand have?

The New Zealand Government acquired significant Bailey bridge stocks after the Second World War for use by the Ministry of Works. Custodianship of these stocks over time has transferred to Waka Kotahi.  At the start of 2023, Waka Kotahi held around 20 Bailey bridges available for immediate deployment (with each bridge being 30m).

Waka Kotahi considers that the existing supply will be sufficient to meet the needs of the initial emergency response, based on information currently available. If the need arises as we progress through the recovery phase, Waka Kotahi will procure more stock. We are also investigating other temporary bridging solutions, to respond to the recovery phase of the cyclone and enhance our ability to respond to future events.

How are sites being prioritised for bridge installation?

NEMA, supported by Waka Kotahi and impacted local roading authorities, have compiled a list of bridges that have been prioritised as high (urgent), medium, and low priority based on the following criteria: connecting isolated communities; current supply chain; and length of bridge vs benefit. Additional bridges which require prioritisation are currently under discussion awaiting further information from the relevant local authorities.

The above diagram outlines the process of damage assessment, prioritisation, site preparation and installation.

Where are the bridges being installed?

Waka Kotahi is reporting on Bailey bridge installation on the state highway network in the table below.

Bridge Name Road Controlling Authority Road Name Status Expected Bridge Opening Date*
SH35 Hikuwai No. 1 Bridge Waka Kotahi SH35 Site Works Underway Late May
SH2 Waikare River Bridge Waka Kotahi SH2/Napier-Wairoa Road Site Works Underway Mid-April

Councils are reporting road closures statuses, including affected bridges, on local road networks. Updates can be found from the council websites below.  

How quickly can a Bailey bridge be installed?

Whether Bailey bridges can be installed, and how quickly they can be set up, depends on how accessible the location is and how much work needs to be done to prepare the site. For example, sometimes piers (the support columns a bridge sits on) may need to be built to support the bridge, which can make installation take longer.

While establishing a Bailey bridge at a site can take as little as a few days for a short span, there could be weeks of site works involved prior to the Bailey being able to go in. There may need to be piers constructed, the surrounding roads rebuilt, or we need to wait for water levels to go down. Sometimes contractors cannot physically get the components to site until the surrounding roads are fixed. It’s important to note that sometimes installation may not occur till months after a need is identified.

Who does the engineering and installation work?

Waka Kotahi manages a national supply of Bailey bridges and has a contract with Downer for the installation of the superstructure.

The road controlling authority is required to design and build the approaches and substructure for the bridge. These are typically undertaken by the Authority’s design consultants and roading contractors.

Are there weight or size limits on Bailey bridges?

Bailey bridges are generally designed to accommodate all road legal vehicles, not just light traffic, but on occasion they may have vehicle weight restrictions.