Driver Knowledge Tests

What are higher mass limits (HML)?

To make road freight as efficient as possible, higher mass limit laws were created. These increase the maximum weight limits for trucks to allow more freight to be moved on one vehicle. However, more weight means potentially more damage to the road’s surface, so there are restrictions on the specifications of the vehicles.

All vehicles must be fitted with certified road-friendly suspension. This is suspension that cushions the impact of the load, reducing vibration that degrades road surfaces and bridge structures.

Vehicles must only operate on an authorised HML route (or have the correct permit to operate outside the HML route). Maps can be found for each region, for example, here is the NSW map for B doubles, or you can use the NHVR route planner tool which shows approved routes for use by B-doubles, B-triples, HML, performance-based standards (PBS), road trains and some commodify routes.

Vehicles or combinations running on tri-axle groups are accredited under the Mass Management Module of the NHVAS (National Heavy Vehicle Accreditation Scheme) and have an accreditation label fitted to the hauling unit/prime mover.

There are minor variations to policy in some states and transitional notices should be checked before making assumptions.

In some states (e.g. NSW and QLD), operators must participate in the Intelligent Access Program (IAP).

Maximum mass per axle group

TYPE OF AXLE GROUPMAXIMUM MASS (TONNES) PERMITTED UNDER GMLMAXIMUM MASS (TONNES) PERMITTED UNDER HML
Tandem axle group16.5t17t
Tri-axle group20t22.5t
Single drive axles on buses9t10t
Six-tyred tandem axle groups13t14t

If an operator wants to use a vehicle outside of the permitted road network, or the vehicle configuration is not covered by a notice, they can apply for a permit.

Darren is an expert on driving and transport, and is a member of the Institute of Advanced Motorists

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