A wheel snapped off a trailer near Cromwell in 2017, flying into Lake Dunstan. Photo: Supplied
Wheels snapping off mobile school dental clinic trailers are not just a danger on the road, but it turns out have got in the way of looking after children's teeth.
Emails and reports released under the OIA to RNZ show one dental service pleading to find out where an investigation into the threat has got up to.
That investigation is still not finished, more than two years after a wheel flew down Tauranga's main street.
"The wheel crossed one lane of same direction traffic, hit the centre island and bounced over the top of two lanes of opposing traffic, it narrowly missed patrons outside the K Sushi Shop before hitting the wall of Beaurepaires Tyres," a complaint lodged last year with Waka Kotahi said.
The OIA response shows the safety response has been slow and patchy.
Heavy wheels have twice snapped off the 4.6-tonne trailers, on the highway outside Cromwell in 2017, and in 2020, in Cameron Rd, Tauranga.
Twenty months later, in March this year, Lakes DHB community oral health services emailed Waka Kotahi desperate for information.
It was still having to shift the trailers around on the back of a truck instead of towing them, it said.
"Moving such large units via a low-rider [truck] also has significant risks and sometimes our dental units are being damaged during loading and unloading", it said.
"When combined with our limited budget and stretched resources, this is impacting our ability to deliver oral health services to children."
The dental service pointed out "NZTA were informed of the incident almost immediately" more than 18 months before.
"Your report is important to assist us with planning a way forward," the service told Waka Kotahi.
"Please let me know if there is any information from anyone that you are awaiting for.
"If you are unable to provide an estimated time could you advise me of someone to whom I can escalate my request?"
There is no record of NZTA responding in any substantive way.
The agency began its investigation into the Tauranga snap-off in June 2021, 11 months after it happened.
That investigation is still going on.
"Information provided to Waka Kotahi has evolved over time," it told RNZ last week.
"Waka Kotahi is currently finalising the investigation report due to new information that has recently been provided by the manufacturer and a heavy vehicle specialist certifier.
"This information includes in-depth, complex testing that is almost completed and should provide possible solutions."
Police had tested the Tauranga trailer way back in September 2020.
Their vehicle safety experts told NZTA then that weaknesses in how the wheels were bolted on were likely to blame.
"The wheel nuts may be too small for the wheel loading," the police said.
"The wheel does not fit closely over the hub therefore not supported by the hub."
A few weeks later, Waka Kotahi visited the trailer-maker, Action Manufacturing of Hamilton.
It did not investigate, but asked about Action's investigation.
"Conversations were held with several parties," the agency told RNZ.
For the next two years, 23 of the 4.6-tonne trailers remained in service nationwide, until a safety alert in September this year told dental services to check the wheels, and be "vigilant" towing them.
The alert was issued not by Waka Kotahi, but by Health NZ Te Whatu Ora.
The large trailers with clinics inside are not moved much, just between schools.
The two that failed had done less than 2000km when the wheel studs sheared completely off.
In Tauranga, "the wheel came off less than 10 minutes after the dental trailer had been collected from VTNZ, after passing a 6-monthly heavy trailer Certificate of Fitness", the company in charge of moving the trailer, Medworx, said in a complaint to Waka Kotahi in June 2021.
"This indicates how undetectable, sudden and catastrophic the failure is."
VTNZ declined to comment.
Medworx's complaint was against the engineer which certified most of the dental trailers, TSV Consultants of Cambridge.
Medworx had also alerted the police, back in September 2020.
Shortly after the Tauranga near-miss, TSV had put out a half-page report saying "no issues" were found with the wheel configuration.
"Faulty components cannot be ruled out, but the issue is more likely around coupling tow height and maintenance", TSV said.
This infuriated Medworx, the OIA documents show; it also runs counter to the police tests of the trailer in September 2020, that discounted tow height.
TSV Consultants told RNZ: "It is important to us to find the cause of the failures as safety is at the forefront in all we do.
"We do now believe we understand the reason/reasons for the failures and are now working on a fix which will be rolled out across the trailers in the near future."
It remains unclear why Waka Kotahi waited until the Medworx complaint in mid-2021 to begin its own investigation.
Health authorities appeared in no doubt in September 2022 what the problem was.
"Enquires and subsequent incident investigations concluded that the incorrect wheel assemble [sic] was attached to the hub resulting in the sheering [sic] of the wheel studs while being towed," Te Whatu Ora said.
"The original manufacturer refutes there is a design issue and rather cites a towing operator error. This hypothesis has been refuted by several engineering reports and the NZ Police report."
Action Manufacturing told RNZ it was working with Waka Kotahi and certifiers.
"Action remains openly committed to the investigation and takes all matters of safety seriously," the company said.
"It's a complex investigation with multiple parties committed to ensuring the correct outcome."
Timeline from OIA documents
2013 - Dental trailers manufactured
2017, July 21 - Wheel snaps off trailer near Cromwell, flying into Lake Dunstan
2020, July 14 - Wheel snaps off trailer in Cameron Rd, Tauranga
September - Police test trailer, raise doubts about how wheels attach
October - Waka Kotahi first alerted
Nov 13 - Waka Kotahi visits manufacturer
2021, June - Trailer mover Medworx lodges complaint; Waka Kotahi begins investigation
2022, March - Lakes DHB pleads for info from Waka Kotahi
July - Medworx warns trailer problems remain
September 27 - Te Whatu Ora issues safety alert
December - Investigation carrying on