Heavy haulage operators are expressing concern that newly constructed bridges on key Recent Zealand highways are unable to accommodate their largest loads, forcing costly and time-consuming detours. The issue centres on three recently opened bridges – the Mangaharakeke bridge on the Waikato Expressway, the Puhoi Viaduct on State Highway 1, and the Manawapou Bridge on State Highway 27 – which have weight restrictions preventing the heaviest trucks from using them.
Jonathan Bhana-Thomson, chief executive of the Heavy Haulage Association, said his members were surprised to discover the limitations. “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 gain the heaviest loads over them,” he explained. “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.”
The restrictions force heavy haulage trucks to detour through Hamilton city or along the older section of State Highway 1 at Puhoi, adding significant time to journeys. Bhana-Thomson said the association sought clarification from Waka Kotahi NZ Transport Agency but received no clear explanation for the weight limits.
The core of the problem, according to Bhana-Thomson, may lie in the bridge design standards, which are based on a manual dating back to 1972. “They didn’t anticipate all of the vehicles that would demand 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.”
The concerns extend beyond existing bridges. Dom Kalasih, head of Transporting NZ, which represents High Productivity Motor Vehicle (HPMV) operators, expressed surprise at recent changes to bridge load calculations issued by Waka Kotahi in January. He fears the agency may not have fully considered the industry’s long-standing calls for a more robust highway system. “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.”
Waka Kotahi issued new calculations for bridge loading in January as part of an overhaul project that began in 2022. According to agency notes, the changes provide a “far better” picture of how trucks impact bridges, including convoys. However, the agency told RNZ that the changes would result in only “small design changes” for new bridges. Kalasih criticized this approach as a missed opportunity to future-proof infrastructure. “Because if it’s not going to make much difference, how is it better?”
Transporting NZ had advocated for new bridges to be designed to accommodate maximum loads of 62 tonnes, exceeding the current HPMV limit of 58 tonnes. While acknowledging the increased cost, Kalasih argued that investing in productive infrastructure was essential. “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.”
Waka Kotahi stated that 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 and Kalasih remain unconvinced, fearing a conservative approach that could hinder productivity.
The debate over bridge capacity comes after the Infrastructure Commission’s annual report highlighted New Zealand’s lagging performance in infrastructure development compared to other OECD countries. Waka Kotahi has acknowledged that its current bridge design model “has reached its limits in terms of providing for future growth” and that some existing bridges may be “unconservative” in their load-bearing capacity.
Waka Kotahi has stated that it is not anticipating widespread changes to weight limits on existing bridges and that no repair or upgrade work is currently planned to address the new load calculations. However, Bhana-Thomson warned that even a single down-rated bridge on a critical route could disrupt the entire network. The Heavy Haulage Association plans to contact Waka Kotahi’s structural engineering team to ensure that the Roads of National Significance projects are designed to accommodate specialist overweight loads, and if necessary, escalate the issue to the Minister of Transport.
