Source: Radio New Zealand
Close up of a truck wheel. siwakorn / 123RF
Truckers are worried that they will not be allowed to drive over bridges being built on the government’s Roads of National Significance.
Two bridges built recently on State Highway 1 in Auckland and a third in Waikato are off limits to the heaviest haulers.
They are also concerned by the way NZTA Waka Kotahi is overhauling the country’s half-century-old bridge design model.
Heavy Haulage Association Jonathan Bhana-Thomson says his members’ huge trucks transported the massive beams that hold up the three highway bridges built near Hamilton, Puhoi and Matamata in the past three or four years – but they did not realise they would never even get to drive over the bridges.
“The beams on the Waikato Expressway and the Puhoi, so all those would have been constructed somewhere else and then transported there by members of our association, of our industry, that now can’t get the heaviest loads over them,” said Bhana-Thomson.
“For them to be limited for, yes, they are heavier loads, but for us to have to detour off those onto essentially lower graded State Highway routes was a real surprise for us.”
Heavy Haulage Association. chief executive Jonathan Bhana-Thomson. RNZ / Phil Pennington
The bridges are:
- Mangaharakeke bridge on the Hamilton section of the SH1 Waikato Expressway – opened July 2022
- Puhoi Viaduct on the SH1 Northern Gateway Toll Road – opened June 2023
- Manawapou Bridge on SH27 – opened April 2022
The laden trucks instead had to detour through Hamilton city or the old SH1 at Puhoi, said Bhana-Thomson.
“So it takes a lot longer.”
The truckers asked the transport agency how this came to be, but remained none the wiser.
“They didn’t anticipate all of the vehicles that would need to go over it, including our specialized overweight ones.
“Possibly at the heart of that is… they’re relying on the bridge manual that was determined in 1972 and the vehicles that were around at that time.”
That bridge manual sets the rules around the models of bridge design and how to assess how to build stronger to last longer, or to determine what is too weak.
Bhana-Thomson only found out from talking to RNZ last week about NZTA’s latest design moves – when it issued in January some new ways to calculate loads – and did not like what he read in NZTA’s notes and statement.
Transport NZ head Dom Kalasih was also surprised to learn of the January change from RNZ, and it suggested to him that NZTA might not have taken on board his industry group’s years of campaigning for a more thought-through system of better, stronger highways overall.
“If you go and put a bridge in a place where that is the constraint, that’s the choke point,” Kalasih said.
“If a truck can’t bypass that bridge relatively easily, right, then it’s got to take an alternative route for that journey.”
Transporting NZ represents the next heaviest lot of truckers, High Productivity Motor Vehicles (HPMV trucks) with specific permits that boost them from 44 tonnes to 58 tonnes. They number in the thousands – while perhaps only 200 heavy haulers operate on any given day – on both long-haul down-island routes and, more commonly, doing inter-region hauls of supplies like fuel and food.
Kalasih voiced fears that NZTA was going to be too conservative again, like at Puhoi and the Mangaharakeke bridge, even though the government’s RONS aims seemed to demand that productivity be put on par with durability.
The bridge debate comes just after the Infrastructure Commission put out its annual report, which said New Zealand was worse than most OECD countries at building, upgrading and managing infrastructure.
The bridge manual itself has not had a complete overhaul in half a century.
NZTA had acknowledged it had “reached its limits in terms of providing for future growth”.
“The model also has specific scenarios where the loading is known to be unconservative” – which means that some bridges did not have enough leeway for carrying big trucks.
Kalasih said trucks were bigger and better designed, and trucks with larger loads had them better spread over more axles to spread the weight, but bridge design standards had not kept pace with that reality.
The latest new calculations on bridge loading were issued in January under an NZTA overhaul project, which has been underway since 2022.
In its notes to engineers in 2022, NZTA talked about “extensive” changes being brought in to load calculations.
It also said it gave them a “far better” picture of how trucks impacted bridges, including convoys of trucks.
But the agency told RNZ that for new bridges, it meant only some “small design changes”.
“The measures being introduced are primarily an update of existing rules and regulations and are not anticipated to have a significant impact on existing bridge stock or the construction of new ones,” it said.
Kalasih said this was a real missed opportunity to futureproof bridges. “Because if it’s not going to make much difference, how is it better?”
Transporting NZ had made submissions that new bridges should be able to take maximum loads of about 62 tonnes in future. That would cost more than building to the current HPMV limit of 58 tonnes, but “the public has to pay for the infrastructure regardless. So they can either pay for it to be done unproductively or they can pay to get it done productively”.
NZTA told RNZ the new measures were “a response to changes in bridge designs (longer continuous spans) and to accommodate the heavier trucks that are now more common on New Zealand roads and highways”.
Bhana-Thomson was not reassured by that, and shared Kalasih’s fear that transport authorities were being overly conservative.
NZTA’s approach to pulling bridge design into the new century seemed to leave heavy haulers out of the picture, contrary to what they were promised months ago, he said.
“That’s what they’ve said to us. But we have no proof of it.
“It is concerning, especially because we’ve got the new roads of national significance being constructed and designed right now,” he said.
“These will be the ones we’re using for the next 50 years, so we need them to be up to standard.
“We will contact the structures people in NZTA to ensure that the roads of national significance will be modelled for our specialist overweight loads.”
If that did not work, they could go to the minister, he said.
The NZTA notes said “extensive amendments have been made to the live loading and evaluation process for determining the capacity of existing bridges”.
“The loads are more complicated than previously used but will far better replicate heavy vehicle traffic on the highway network.
“It is possible that there will be a number of bridges on the network where the capacity is found to be less than currently known and these findings will need to be managed.”
But the agency also told the industry it was not intended that large numbers of existing bridges “will suddenly need new posted weight limits”.
And it told RNZ: “For old bridges there is currently no repair or upgrade work planned or underway to address these changes.”
Bhana-Thomson pointed out it would only take one bridge on a busy truck route to be down-rated for it to potentially throw the whole route into disarray.
Kalasih also said this was an issue: “In the absence of any further information, my initial reaction is, yes, one of concern, that bridges will be downrated.
“That’s certainly a risk.”
The transport agency emphasised to RNZ in its statement that it had a programme of routine maintenance, inspection, strengthening and replacement that gave it a good picture of the state of all bridges, with safety its number one priority.
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– Published by EveningReport.nz and AsiaPacificReport.nz, see: MIL OSI in partnership with Radio New Zealand
