The mobile dental clinic, minus a wheel, is loaded on to the back of a truck near Cromwell. Photo: Supplied
The Transport Agency says it is investigating why heavy wheels have twice flown off mobile dental clinics, endangering other motorists.
RNZ revealed on Friday Waka Kotahi received a complaint months ago claiming the large, caravan-like clinics are not safe to tow.
Health New Zealand has already warned hospitals the failures in 2017 and 2020 were due to incorrect wheel assemblies, and is telling them to check all two dozen vans and perhaps take some off the road.
But Waka Kotahi said today it was still working "to determine the root cause of the issue, and whether possible solutions are required".
It had a heavy vehicle specialist certifier undertaking "lengthy system modelling" - the same certifier the complaint was about in July 2021 - it said in a statement, its first public comment on the wheels flying off.
The certifier was working with the trailer-clinic's manufacturer.
The manufacturer told RNZ on Friday the wheels were assembled according to the specifications of the supplier of those parts.
"The trailers have been cleared independently by NZTA-qualified engineers," the manufacturer, who RNZ is not naming at this stage, said.
Waka Kotahi said it first became aware of wheels snapping off their studs following the second case in Tauranga in July 2020.
"At that time, conversations were held with several parties to understand what they'd found from their own investigations and what action was being taken as a result.
"We were informed that the vehicle components were compatible and rated appropriately but may have been impacted by other contributing factors, including vehicle loading, tow coupling height, wheel torque, and how the vehicle is manoeuvred into location."
There have been conflicting engineers' reports about the cause.
A second certifier who had a look at the broken Tauranga clinic in 2020 said he was "duty bound to inform NZTA" urgently "because of the critical public safety aspects".
Waka Kotahi said both the manufacturer and original certifier had issued advice on checking trailers before each use.
It had heard from the police and Canterbury District Health Board, among others, it said.
"Waka Kotahi has a regulatory role to play in this matter and we are concerned about road safety matters. We are unable to comment on interactions or roles of other parties."
All the wheel studs were shorn off at the Cromwell dental van accident in 2017. Photo: Supplied