The surprise announcement by NSW and SA to allow low- and zero-emissions trucks to exceed regulated axle load limits on state roads offers game-changing opportunities for the road transport industry and its efforts to decarbonise freight
It’s often said the only constant is change. When it comes to truck axle load limits, that hasn’t historically been quite true.
The past few decades have seen only marginal increases to axle load limits, despite vast improvements in vehicle safety and emissions technology, which often bring a tare mass penalty.
This has the unfortunate impact of gradually eroding truck productivity over time, making it harder and harder for the industry to do what it does.
If you asked the nation’s truck operators what regulatory changes would bring seismic improvements to their businesses, increases in axle load limits would undoubtedly be in the top three.
But right now, there are two much-needed changes in the works. One directly addresses the productivity erosion issue via marginal increases, while the other could offer revolutionary opportunities for the decarbonisation of freight transport in this country.
In the margins
Decades ago, mass limits were set at six tonnes for a single steer axle, and 11 tonnes for a twin steer axle.
They still remain at those limits today, with some exceptions. The most important of those was the change in 2006 to allow an extra 500kg for the single steer axle of trucks fitted with Euro IV emissions compliant engines, and a range of safety technologies. That extra 500 kg went some way to offsetting the tare mass penalty of increased safety and emissions performance.
Crucially, twin steer axle trucks missed out on additional mass; an unfortunate and unnecessary omission that tilted the playing field to their disadvantage.
Truck engine emissions reduction technology has advanced considerably in the seventeen years that have elapsed since.
Australian Design Rule 80/04, the latest regulatory instrument that covers truck emissions, was signed in February this year and will require all trucks with a gross mass over 3.5 tonnes that are supplied on or after November 1, 2025 to achieve Euro VI emissions compliance. Euro VI has, and will continue to, bring further increases to truck tare mass as it is continually rolled-out by manufacturers.
Despite being mandated, the tare mass increases of Euro VI compliance have not been offset in any meaningful way. Until now. It’s often said that while history doesn’t repeat itself, it often rhymes. Again, when it comes to truck axle load limits, that’s unfortunately not true either. History is certainly repeating itself now.
Early this month, the National Transport Commission released its Consultation Regulatory Impact Statement (C-RIS), which is essentially a proposal for options to improve specific areas of the Heavy Vehicle National Law.
Importantly, one of the options is to grant an additional 500kg for the single steer axles of trucks complying with Euro VI, offering much-needed concessions to offset the tare mass penalties currently carried.
Sound familiar? This would bring the mass limit for single steer axles (in HVNL signatory states) to a much-needed seven tonnes.
Crucially, the only mention in the NTC’s document given to increases for twin steer axles states that an appropriate mass limit increase has not yet been determined.
There is no justifiable reason why twin steer axles should not be given an additional one tonne – 500kg as recompense for missing out on the Euro IV increase, and the same 500kg proposed for single steer axles.
Talkin’ about a revolution
In complete contrast to these marginal gains, which were often the result of months of discussion and debate between industry, regulators, and road managers, the sudden announcement of what is essentially an axle mass revolution has caught many industry stakeholders by complete surprise.
In early October, two states announced plans to allow low- and zero-emissions trucks to exceed regulated axle load limits on state-managed roads.
The Department for Infrastructure and Transport in South Australia (DITSA) and Transport for New South Wales (TfNSW) each separately announced their own trial schemes. A summary of the major changes proposed by each state to axle mass limits is shown below.
| South Australia | Single steer, tandem drive prime movers: Single steer axle – up to 7.5 tonnes Tandem drive axle – up to 18.5 tonnes Twin steer, tandem drive prime movers: Twin steer axle – up to 12.0 tonnes Tandem drive axle – up to 17.0 tonnes |
| New South Wales | Single steer, tandem-drive prime movers: Single steer axles – up to 8.0 tonnes Tandem drive axles – up to 18.5 tonnes |
While further details were scarce, these two announcements offer game-changing opportunities for the industry and its efforts to decarbonise freight.
Just like the necessary increases to axle mass limits to offset emissions compliance and safety performance, truck manufacturers have long indicated that current axle mass limits are too low for future models and will profoundly hinder the transition to low- and zero-emissions vehicles if not adequately addressed.
Movin’ on up
In that context, it is encouraging to see state road managers proactively responding to the decarbonisation challenge with initiatives like this.
Importantly, the announcements appear to reverse the historic trends of increases to axle mass limits only being allowed after intense and time-consuming lobbying by industry.
Road managers have historically opposed such increases due to Australia’s road construction methods.
Most of Australia’s roads are what’s known as ‘sprayed seals’ which are a thin road type that is relatively cheap and easy to construct yet is suitable for our traffic mix and environmental conditions.
The downsides are a susceptibility to increases in applied load, which can cause accelerated wear.
The reasons behind this sudden step-change are not worth unpacking. It’s much more productive to look at the road ahead.
The best immediate outcomes include the expansion of these schemes to other state roads, and local council roads; minimal deviation in the details and conditions between different jurisdictions; and road access networks aligned with those for ‘ICE-equivalent’ vehicles.
