What is an axle group and how do axle-spacing limits work?
Short answer
An axle group is a legally defined set of closely spaced axles, and a heavy vehicle must comply with both the limit for each axle or group and the separate gross-mass limit produced by its axle spacings.
Plain English
The HVNL defines axle groups such as tandem, twinsteer, tri-axle and quad-axle groups by the number and spacing of their axles. Schedule 1 then assigns mass limits according to axle-group type, tyre arrangement and other conditions.
A second check applies to the distances between axles or groups. The applicable axle-spacing table can impose a lower gross mass than the sum of the individual group limits. If two axles that are not in the same axle group are less than 2.5 metres apart, the current general rule limits the heavy vehicle to 15 tonnes unless another lawful provision applies.
What this means operationally
Identify each legal axle group, measure centre-line spacings accurately, select the correct vehicle or combination table and test every individual axle, group, spacing and gross limit. Keep configuration records for unusual combinations and recheck the calculation when axles, trailers, fifth-wheel position or load distribution change.
Who it applies to
Operators, drivers, loaders, weighbridge staff, fleet engineers and schedulers managing the mass and configuration of a heavy vehicle or combination.
Example
A semitrailer combination can be within the limit for its steer, drive and trailer groups individually but still exceed the axle-spacing gross limit because the distance between the outer groups is too short.
Exceptions and traps
HML, PBS, a mass exception, notice or permit may apply different limits, but only within its exact eligibility, route and conditions. Manufacturer and component ratings can still impose a lower ceiling. The correct table depends on the actual configuration, not the name commonly used for the vehicle.
What changed
From 1 August 2026, GML increased to the former concessional levels for qualifying axle groups. The need to satisfy individual axle, axle-group, axle-spacing, gross and manufacturer limits did not disappear.
Previous rule
Before 1 August 2026, the qualifying dual-tyred tandem and tri-axle GML values were generally 16.5 tonnes and 20.0 tonnes, with the higher concessional figures requiring the former CML pathway.
Legal foundation
Heavy Vehicle National Law ss 5, 95-99; Heavy Vehicle (Mass, Dimension and Loading) National Regulation 2013 Sch 1, including ss 3-5 and the applicable axle-spacing table
Sources & primary documents
- www.legislation.qld.gov.au/view/whole/html/inforce/current/act-2012-hvnlq
- www.legislation.qld.gov.au/view/whole/html/inforce/current/sl-2013-0077
- www.nhvr.gov.au/road-access/mass-and-dimension/mass-limits/general-mass-limits
- www.nhvr.gov.au/document/247
- www.nhvr.gov.au/b-double-axle-spacings-mass-limits
- www.nhvr.gov.au/road-access/mass-dimension-and-loading/road-train-axle-spacing-mass-limits
WWTG verification: Queensland legislation, NHVR
Frequently asked questions
What is an axle group?
A legally defined tandem, twinsteer, tri-axle or quad-axle group whose classification depends on axle number and spacing.
Can I add the axle-group limits to get legal gross mass?
Not necessarily. The axle-spacing table, gross limit and manufacturer ratings may produce a lower result.
Where is axle spacing measured?
The regulation uses axle centre-lines and specifies which centre-lines apply to single axles and axle groups.
What if two separate axles are less than 2.5 metres apart?
The current general rule limits the heavy vehicle to 15 tonnes unless another lawful provision applies.
Does HML remove axle-spacing limits?
No. HML changes eligible axle-group limits but the vehicle must still meet all applicable spacing, route and rating requirements.