The 103-year-old Rawhiti Bridge in Dannevirke will be restricted to light vehicles only from Wednesday 2 September, following engineering advice.

Routine inspections of the bridge had identified cracking and defects that warranted further investigation. An engineering assessment in June indicated structural testing was needed to confirm assumptions about the bridge's condition and strength. Tararua Alliance commissioned a detailed programme of investigations, including crack mapping, concrete core sampling and steel testing.

Those investigations found the bridge is in significantly poorer condition than originally thought, with testing showing substantial deterioration of the concrete deck and supporting beams.

The engineer's recommendation is that the bridge be restricted to light vehicles only at a reduced speed of 30km/hr, and that heavy vehicles cease using the bridge as soon as practical. This means most cars, utes, SUVs and light vans can continue to use the bridge. Trucks, heavy commercial vehicles and heavy haulage vehicles will need to use alternative routes.

Tararua Alliance Network Manager Andrew Desmond says the Alliance is acting on the engineer's recommendation: “The testing found significant age-related deterioration within the bridge structure. Investigations identified low concrete strength in parts of the bridge, accelerated cracking and evidence that the concrete is no longer providing the level of protection to reinforcing steel that would normally be expected. Engineers concluded the bridge is no longer suitable for carrying heavy vehicle traffic and that replacement options should be investigated.”

"This is much shorter notice than we would ideally provide. However, the engineering advice is clear that heavy vehicles need to stop using the bridge as soon as practical. The bridge is safe for light vehicles – this is about slowing further deterioration so it can continue to be used while we investigate long-term options.”

The bridge carries about 970 vehicles a day, of which about 67 are heavy vehicles. Rawhiti Street has been used as an alternative heavy vehicle route for trucks wanting to avoid travelling through Dannevirke's main street, as well as access to the business areas west of the railway line.

The alternative route for heavy vehicles will be via State Highway 2 through Dannevirke or local roads.

Temporary electronic message boards will be installed at both approaches to the bridge, with permanent signage expected to be in place within the coming weeks.

"Tararua Alliance will be preparing a business case for NZTA to investigate funding options for a replacement, as we are also doing with the Alfredton Road Bridge."

Tararua Alliance manages 400 bridges and 77 are over 90 years old. Business cases for both the Rawhiti Bridge and Alfredton Road Bridge replacement projects are expected to be prepared during the current financial year.

You can find the location of the bridge here - Google Map

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FAQs

Why is Rawhiti Bridge being restricted to light vehicles only with a 30km/hr speed limit?

Routine inspections identified defects on the bridge and further engineering investigations were commissioned to better understand its condition. Those investigations, which included crack mapping, concrete core testing and steel testing, found the bridge is in significantly poorer condition than originally assumed. The engineering advice is that the bridge is no longer suitable for heavy vehicle traffic and should be restricted to light vehicles only while longer-term replacement options are investigated.

Is the bridge safe?

Yes. The bridge remains open for light vehicles (up to 3.5 tonnes) under a lower speed of 30/km. The engineering recommendation is to remove heavy vehicles from the bridge and reduce vehicle speeds to help manage risk and minimise further deterioration while replacement options are explored. The bridge will continue to be monitored and regularly inspected.

Why has this restriction been implemented now?

The engineer's recommendation was that heavy vehicles should stop using the bridge as soon as practical. Tararua Alliance is implementing the restriction in response to that advice.

What did the testing find?

The testing found significant age-related deterioration within the bridge structure. Investigations identified low concrete strength in parts of the bridge, extensive cracking and evidence that the concrete is no longer providing the level of protection to reinforcing steel that would normally be expected. Engineers concluded the bridge is no longer suitable for carrying heavy vehicle traffic and that replacement options should now be investigated.

What does the two axle, 3.5 tonne limit mean?

The bridge will be restricted to two axle vehicles with a maximum gross vehicle mass of 3.5 tonnes. This means most cars, utes, SUVs and light vans can continue to use the bridge. Trucks, heavy commercial vehicles and heavy haulage vehicles will need to use alternative routes.

Why is a reduced speed limit being introduced?

Reducing vehicle speeds helps reduce the impact and vibration forces created when vehicles cross the bridge. Engineering advice indicated that a lower speed would reduce stress on the bridge structure and help slow further deterioration while longer-term solutions are developed.

What route should heavy vehicles use to bypass Dannevirke main street?

Heavy vehicles heading north can use the State Highway through Dannevirke or avoid the main street by taking local roads.

Can the bridge be repaired?

The engineering assessment concluded that Rawhiti Bridge is not considered a viable candidate for repair and that replacement options should be investigated. The next step is to develop a business case to determine the most appropriate long-term solution and seek funding support.

Will the bridge eventually need to be replaced?

Based on the engineering advice received, replacement is the option that will now be investigated. A business case will be prepared to assess replacement options, costs, funding opportunities and timing. Any final decision will be subject to funding approvals and the business case process.

How does Rawhiti Bridge compare with Alfredton Road Bridge?

The two bridges have some similar age-related issues. Both structures were built using early concrete construction methods and both have had deterioration associated with ageing concrete. In simple terms, the concrete in both bridges has reached a stage where it no longer provides the same level of protection to the reinforcing steel as it once did, leading to ongoing deterioration over time. Each bridge is assessed individually, and decisions about restrictions and future investment are based on detailed engineering investigations specific to that structure.

Will the bridge continue to deteriorate?

All infrastructure deteriorates over time. Restricting the bridge to light vehicles is intended to significantly reduce the loading on the structure while maintaining access for the community. It isn’t possible to accurately predict the future rate of deterioration. Ongoing inspections and monitoring will continue while long-term options are developed.

How many bridges does Tararua Alliance manage?

Tararua Alliance manages 400 bridges and 157 large culverts across the district. These structures are inspected, monitored and assessed on a regular basis using nationally recognised asset management and engineering standards.

Are there plans for further testing on other bridges?

Tararua Alliance is reviewing a number of bridges identified through its network-wide screening programme. Further investigations will be undertaken where engineering assessments indicate they are warranted.

Is funding available to replace ageing bridges?

Yes. NZ Transport Agency Waka Kotahi provides funding assistance for eligible bridge renewal and replacement projects through the National Land Transport Programme. Replacement proposals must meet funding and business case requirements before funding can be approved.