A mobile dental clinic is loaded on to the back of a truck after its wheel sheared off on a highway near Cromwell in 2017. Photo: Supplied
Waka Kotahi has extended its investigation into wheels snapping off mobile dental trailers to encompass the whole supply chain of trailer parts.
However, it has faced barriers, even into determining if this type of failure is more widespread.
Now, six years on from the first trailer failure, the agency is having to negotiate with the suppliers' lawyers.
This despite two trailers failing, and tests showing the wheels were under such huge stress, especially on cornering, that the studs were prone to fail at just 3000km, instead of hundreds of thousands of kilometres.
"Specific information regarding wheel mounting requirements and compatibility of components could not be obtained from the component suppliers despite best attempts by Waka Kotahi," the agency said in its investigation report.
The problem is the component manufacturers and suppliers are not "regulated parties".
"Waka Kotahi is unable to determine if this type of failure has occurred elsewhere.
"Waka Kotahi will engage with these suppliers through their legal representatives to establish this and determine the risk and any further actions that may need to be explored."
Vehicle failures due to component failure were infrequent, the report said.
Still, the investigation was expanded to look at "the entire situation", including heavy vehicle certification, the manufacture of the vehicles - like trailers - here, and component supply.
The report said Waka Kotahi should:
- Alert the industry to how important it was to check the compatibility of components during manufacture or repairs
- Discuss what roles certifiers and manufacturers had "in failure situations"
- Introduce a framework to investigate failures of components
The wheels snapped off two of the dental clinic trailers, as they were being moved between schools, in 2017 and 2020.
The Transport Agency struggled to pin down the cause, and the trailers have meantime been moved around regularly.
An internal hospital email from mid-2022 released to RNZ said: "NZTA have been underwhelming in their response."
The investigation report, released only last month, found the trailers were up to scratch, properly certified and their design was OK.
But while the individual trailer parts were rated correctly independently, they were incompatible on these particular trailers - dangerously so.
"While these were purchased, installed, and certified as meeting requirements, they have failed once extreme fatigue stresses were applied."
The trailers weigh about five tonnes.
It was "very hard" to predict this type of failure, the report said.
"Vehicle manufacturers purchase components in good faith - they are not expected to test every component bought - this is impossible."
Heavy vehicle engineers were also not required to do in-depth testing on every component combination used, it said.
A series of stop-start investigations since 2017, initially privately done, included the trailer-maker Action Manufacturing suggesting maybe the tow operators were being too rough.
The investigation dismissed that: "The fault is related to component compatibility and not the way they are operated".
Several engineering opinions since 2017 had already called attention to the wheel rims and hub components, but they were not picked up on; the Transport Agency only belatedly became involved and began looking into the issue in 2021.
Doug Moller of Dunedin, who tows two of the trailers around, said for six years his company had done rigourous checks on the wheels at every move. But it remained a risk every time, and he wanted that risk removed for good, he told RNZ.
Internal hospital emails released to RNZ show their dental services facing extra costs - of $16,000 to move the trailers on the back of trucks, to $26,000 to fix them - and discussions about how to recover those costs.
In one, in August 2022, the writer linked to a story about a young girl killed when a trailer disconnected in Northland, and said "similar but different to the dental van potential risk when the van is travelling on the open road. Food for thought".
Last September, Te Whatu Ora told RNZ that all districts would have assessed their trailers by the end of October; in mid-November it said either trailers were not being used, had been fixed or the risks were being dealt with.
However, the email trail shows that just a week later, a health and safety consultant at Lakes District Health, said: "It has been a very difficult mission trying to find out exactly who [sic] and where the dental trailers are located.
"I thought those who had trailers were to provide an update ... a couple of weeks ago about remedial actions."
Another commented that "the hard part was getting someone to take ownership here over the problem".
"What a painful process."
They added that trailers had been assessed and were safe to use - though this was weeks before the Waka Kotahi investigation was complete.
A safety alert to hospitals recommended being "hyper vigilant" about towing, but Waka Kotahi never barred the trailers from the road.
Both it and Te Whatu Ora have referred in public statements to RNZ to operators being told not to tow the trailers, or making changes to make them safe.
But communications released under the Official Information Act are inconclusive about this.
Due to delays getting parts, the trailers are only expected to be fixed this month.
Te Whatu Ora said the manufacturer had not yet contacted Lakes district to tell it not to tow the trailers.
"The inability to move these two mobile units [at Lakes] is having an impact on the delivery of our service, as it is restricting our capacity to see and treat more children.
"This situation could adversely affect the oral health of our children," it said.
The district recently added three, smaller mobile dental units to get to rural communities more easily.