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Heavy vehicle dimensions and measurements

Class 2

The forward distance is the measurement is from the rear axis to the front of the vehicle or its load.

The maximum distance a vehicle or its load may extend forward from the front edge of the driver’s seat (in its rearmost position) is three metres.

On a rigid vehicle that has two axle sets and is steered by the front axle set the front axis is as shown – the centre point of the front axle.

front axis of a light truck

The maximum width allowed for a vehicle (other than an agricultural vehicle) including its load is 2.55m, or 1.275m each side of a longitudinal centre line.

Maximum width for a vehicle

Straps or tensioning devices must not be permanently or rigidly fixed to the vehicle.

The only extra width allowed is:

  1. side marker lamps and direction indicators
  2. collapsible mirrors that extend not more than:
    1. 240mm beyond the side of a vehicle or its trailer; and
    2. 1.49m when measured from a vehicle’s longitudinal centre-line
  3. central tyre inflation system hoses that extend not more than 75mm beyond the outside of the tyre on the drive axles of a heavy motor vehicle
  4. a hubodometer that extends not more than 50mm beyond one side of a vehicle from a non-lifting, non-steering axle whose outer casings are of a light colour, provided the hubodometer is fitted on the axle that causes the least overwidth
  5. cab exterior grabrails that extend not more than 1.325m when measured from a vehicle’s longitudinal centre-line
  6. the bulge towards the bottom of a tyre
  7. trolley bus poles and their safety cables, when extended to collect electric power from overhead conducting wires, provided there is a 2.5m ground clearance outside the body of a bus
  8. cameras or close-proximity monitoring systems mounted on the side exterior of a vehicle that extends not more than 70mm from the side wall of the vehicle
  9. devices for improving the aerodynamic performance of a vehicle that extend not more than 25mm from either side of a vehicle.
Heavy rigid vehicle dimensions

The maximum height from the ground permitted for a vehicle, including its load is shown above at point 2. It is 4.3m including lashings, tarpaulins, straps, chains or covers (load securing devices). The straps or tensioning devices must not be permanently or rigidly fixed to the vehicle.

height restriction sign

When you are driving a heavy vehicle, or any vehicle towing a load, you will need to be aware of signs (such as the one shown on the left) on bridges and other spans across roads indicating a maximum height clearance.

The maximum forward distance for a heavy rigid vehicle without a tow coupling is shown above at point 1, and is 9.5m. If the vehicle has a tow coupling it is reduced to 8.5m.

For a heavy rigid vehicle whose rear-most axle is a non-steering axle, the maximum rear overhang permitted including its load is shown at point 4. It is the lesser of 4m or 70% of the wheelbase.

The maximum overall length for a heavy rigid vehicle including its load when not towing a trailer is shown at point 3 above. It is 12.6m not including collapsible mirrors, or 11.5m if towing a trailer.

A  tandem axle is two axles where the centres are spaced no less than 1 metre and no more than 2 metres apart. A tri-axle set means three axles where the centres of the first and third axels are spaced no less than 2m apart and no more than 3m apart with all axles containing an equal number of tyres and none of the axles being a single standard-tyred axle.

The wheelbase is measured from the rear axis to the centre of the foremost axle. In a tandem axle, as shown above, the rear axis is half way between them. If it was a single axle, the rear axis is where the rear axle is.


Heavy motor vehicles must display two or more approved red reflectors. The reflectors must be at least 30cm2 in diameter and they must be placed at 1.5m above ground level, but not more than 2.1m if 1.5m is impractical.

Class 3-5

The maximum width permitted for a heavy trailer (other than an agricultural trailer) from its longitudinal centre line is 2.55m, the same as other vehicles.

The maximum overall length for a rigid vehicle and semi-trailer combination (including load, but excluding collapsible mirrors) is 19m. If it was with a trailer, it would be 20m. The maximum overall length for any heavy motor vehicle towing two trailers is 20m. This length applies whether it’s an A-train, B-train, pole trailer or simple trailer.

The maximum distance a load may extend behind the body of a trailer before an over-dimension flag is required on the end of the load is 1m. There are different lighting requirements depending on the dimensions of the load. At night the flag must be replaced by one or more lights, depending on the characteristics of the load. If the load is up to 1m long and more than 1m wide then you only need one rear-facing red light in the centre of the load.

Heavy motor vehicles and vehicles fitted with a flat deck or tray for carrying goods that are parked on the street at night must display a rear-facing red light that is visible at least 100m away and is on the side of the vehicle closest to the centre line. If it’s an over-dimension vehicle (i.e. one with a projecting load) then the lights must be visible from at least 200m away during the hours of darkness.

Full trailer dimensions

Rear overhang means the distance from the rear axis to the rear of the vehicle or its load, whichever is greater. The maximum for a heavy full trailer is 4 metres or 50 percent of the wheelbase, as shown in the diagram above, whichever is less.

For a semi-trailer, forward distance means the distance from the rear axis of the semi-trailer to the centre of the kingpin. The maximum is 9.2 metres.

Semi trailer dimensions
A-train dimensions
B-train dimensions

For a towing vehicle and full trailer combination (including the load if the load overhanging the rear of the trailer does not exceed 2.3 metres in width, or 1.15 metres from the longitudinal centre-line of the vehicle) the maximum overall length is 22 metres.

Truck and simple trailer combination (one axle set on the trailer

Full weights and measures can be found here.

See if you know your class 2 measurements: take a free quiz here.

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Darren has written over 3000 articles about driving and vehicles, plus almost 500 vehicle reviews and numerous driving courses. Connect with him on LinkedIn by clicking the name above

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