An investigation into a big double-trailer truck losing half its heavy load on a highway shows it was not a one-off accident.
The front page of the Waka Kotahi report into the investigation into a big double-trailer truck losing half its heavy load on State Highway 70, inland from Kaikōura, in January 2020. Photo: Screenshot / Waka Kotahi
Investigators identified that welds on almost half - 42 percent - of trailers with this same "unconventional" design had failed at one time or another.
The report has finally been released by Waka Kotahi after RNZ asked for it almost a year ago.
It shows defective welds combined with poor design, in the failure that dumped the entire refrigerated body off the rear trailer of a B-train truck on to State Highway 70, inland from Kaikōura, in January 2020.
Read the full MaxiTrans, Refrigerated Rear Trailer - Body Separation report (PDF, 6MB)
The title-page photo shows cars manoeuvring around the box the size of a shipping container.
"Connections of the same design regularly failed and were undetected by normal vehicle inspection and [truck] CoF inspection as the fault was difficult to identify," the report, completed in March this year, said.
The boxes were held to the trailer by the welds alone.
"There appears to be no consideration given to any weld defects or fatigue" in the Heavy Vehicle Rule, the report said.
The trailer design meant the welds were in a spot that was difficult for inspectors to check.
The connection was not one of those covered by the rigourous checks performed by certifying engineers, as opposed to less well qualified VTNZ-style inspectors.
"MaxiTrans appear to have a high reliance on New Zealand's Heavy Vehicle Certification process, however the welded connection at this point is not subject to Heavy Vehicle Certification."
The trailer-maker cooperated and acted quickly to get all the truck-trailers fixed, Waka Kotahi said.
However, the investigators said the evidence did not support a claim that welding standards had been adhered to.
"The manufacturing check sheets provided do not appear to be specific design controls, welding controls or qualified welding inspections and appear more generic and appearance-focused.
"MaxiTrans have not demonstrated or provided information which describes the use of a quality control system with robust and specific gates to control the quality of design and then fabrication."
MaxiTrans said it had introduced more quality checks.
There was also a lack of maintenance and servicing information, the report said.
"Including an inspection point for the unconventional connection in the required information may have aided early detection of failure."
After the box fell off, Waka Kotahi advised vehicle inspectors to look at welds more carefully.
The investigators recommended the agency issue MaxiTrans a warning letter reminding them they must abide by mandatory legislative rules.
They also recommended that Waka Kotahi look at introducing certification around how refrigerated boxes are attached, when a trailer lacks certified anchorage points.
It is unclear where the agency has got to on that.