Industry Insights

Dimensions: Beginners guide

DimensionsWhen you consider the sheer size and weight of a heavy duty truck, loaded with freight and moving at speed, it’s easy to understand why there are regulations and requirements around on-road variables like loads, restraints and dimensions.

Our roads are a shared place, so to ensure the safety of all Australian road users as well as the longevity of our road infrastructure, the Heavy Vehicle National Law (HVNL) was put in place back in 2014.

Administered by the National Heavy Vehicle Regulator (NHVR), the law covers all heavy vehicles over 4.5 tonnes Gross Vehicle Mass (GVM) in Queensland, New South Wales, Victoria, Tasmania, South Australia and the Australian Capital Territory.

A significant part of the HVNL relates to regulations around prescribed dimensions for heavy vehicles.

This blog is an introductory look at what those regulations are, why they’re necessary and what happens if truck owners don’t comply.

What are they?

In very basic terms, ‘dimensions’, (as they apply to HVNL), refers to the length, width and height of heavy vehicles (over 4.5 tonnes), as well as the variety of different trailers attached to those vehicles.


Depending on the vehicle and trailer combination you have in place, regulations apply to ensure your combination is safe to operate alongside other road users and won’t damage the road infrastructure it will be travelling on.

Dimension limits at a glance

  • The width limit for heavy vehicles (over 4.5 tonne GVM) is 2.5 metres
  • Height limit is set at 4.3 metres with some exemptions for certain trailer types such as livestock trailers (4.6 metre limit)
  • Overall combination lengths are a little more complicated because these limits are linked to axle groupings and trailer types.  However, common length limits are:
    • 12.5 metres For any rigid truck and most rigid buses
    • 19.0 metres for any truck and single trailer combination (including semi-trailers)
    • 26.0 metres for a B-Double combination
    • 53.6 metres for a class 2 BAB Quad Road Train
  • Rear overhang is restricted on trucks to 60% of the wheelbase or 3.7 m, whichever is shorter.
  • Finally, some special vehicle combinations are permitted to exceed some of the general dimension limits through a scheme called Performance Based Standards (PBS). The PBS scheme is complicated, but ensures longer or heavier vehicles attain superior levels of safety as well as allowing for improved productivity.

For a comprehensive rundown on prescribed dimensions including trailer lengths and rear overhang (the ‘rear overhang’ of a vehicle is the distance between the rear of the vehicle and the rear overhang line of the vehicle), we recommended you check out the NHVR’s National heavy vehicle mass and dimension limits fact sheet.

Fines and penalties

Getting to grips with exactly what dimensions your truck(s) should be whilst operating on Australian roads will go a long way to helping avoid costly penalties, some of which could leave you up to $10,000 out of pocket.

Chapter four of the HVNL’s Schedule of Penalties, Infringements and Demerit Points covers vehicle operations for mass, dimensions and loading. The schedule is updated annually and covers each type of penalty in some detail as they relate to the Heavy Vehicle National Law (HVNL).

In summation, and as the saying goes, ‘knowledge is power,’ so before you hit the road again, head a potential fine off at the pass and ensure your truck or fleet is compliant.

To find out the more about Isuzu truck dimensions, download spec sheets and chassis drawings for our latest truck models.