Information for heavy vehicle drivers

Heavy combination motor vehicle types

Full trailers

Full trailer

Full trailer

Axles

A full trailer has two axle sets, one of which is connected to the towing vehicle by a drawbar that steers the front axle set.

Note: the axle set requirements described here apply to heavy trailers. They don't apply to light trailers (that is, trailers with a gross vehicle mass (GVM) of up to 3.5 tonnes).

A heavy full trailer must have a front axle set consisting of either:

  • a single axle set, or
  • a tandem axle set.

A heavy full trailer must have a rear axle set consisting of either:

  • a single axle set, or
  • a tandem axle set, or
  • a tri-axle set, which is only permitted if the front axle set is a tandem axle set.

Overall length

The maximum overall length for a full trailer (including drawbar and load) is 11.5 metres.

For a rigid vehicle and full trailer combination (including load, but excluding collapsible mirrors), the maximum overall length is 20 metres.

Forward distance

For a full trailer, forward distance means the distance from the rear axis to the front of the trailer (excluding the drawbar and front axle set) or its load, whichever is foremost. The maximum distance is 8.5 metres.

Rear overhang

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, whichever is less. The maximum overhang for a light trailer is 4 metres.

Wheelbase

The wheelbase of a full trailer is the distance from the rear axis of the trailer to the centre of the front axle set of the trailer.

Front overhang

For full trailers, front overhang means the distance from the centre of the turntable that connects the front axle set to the chassis of the trailer, to the foremost point of the vehicle (including its load, but excluding the drawbar). The maximum is 2.04 metres radius arc ahead of the turntable centre.

Tow coupling

For a rigid vehicle towing a heavy full trailer, the tow coupling position must not be further behind the rear axis of the towing vehicle than a distance equal to 45 percent of the wheelbase of the rigid vehicle.

Inter-vehicle spacing

For full trailers, inter-vehicle spacing means the distance between the towing vehicle (excluding the tow coupling shroud) and the trailer (excluding the drawbar but including the load). The maximum distance is 4 metres. Full trailers also have a minimum inter-vehicle spacing of either 1 metre or half the width of the foremost point of the trailer (including the load but excluding the drawbar), whichever is greater.

Width

This is the same as for heavy rigid vehicles (see page 206).

Drawbars

A drawbar on a full trailer can only have one operating position and cannot be extendable, unless it complies with one of the following:

  • it may only be retractable to facilitate loading or unloading of livestock or goods, provided that the drawbar has only one set of holes for locking pins and these holes are positioned so that the drawbar is fully extended when locked, or
  • if the trailer is used to transport logs, the drawbar may have up to three fixed positions and one sliding position, provided that the drawbar has:
    • one sliding position for long logs, and
    • one or two fixed positions for short logs, and
    • a fixed position for storage of the drawbar when it is out of use while the trailer is being transported on a rigid vehicle or another vehicle.

Note: when fully extended, the drawbar dimension must be such that the length of the trailer does not exceed 11.5 metres and the total length of the combination vehicle does not exceed 20 metres.

Drawbeam

A drawbeam must not be sliding or adjustable.

Gross mass

The maximum gross mass of a rigid vehicle and one full trailer in combination is 39 tonnes, unless the towing vehicle has:

  • a twin-steer axle set or a wheelbase of at least 4.25 metres, and
  • at least two motor-driven axles in the rear set of the truck.

In addition to these two conditions, the maximum gross mass of the heavy full trailer vehicle must not exceed 42 tonnes, unless:

  • the towing vehicle has a twin-steer axle set or a tri-axle set, or
  • the trailer has two tandem axle sets or the trailer has five axles.

Semi-trailers

Semi-trailer

A semitrailer with a quad axle set and two steering axles is limited to 18 metres.

Axles

A semi-trailer has one axle set, attached to the towing vehicle at one of these two coupling positions:

  • at or forward of the rearmost axle of the towing vehicle (for rigid vehicles with one axle in their rear axle set or where another trailer is the towing vehicle), or
  • not more than 300 millimetres behind the rear axis of the towing vehicle (for rigid vehicles with two or more axles in their rear set).

Note: trailers attached to the towing vehicle behind the above positions are considered simple trailers (including Stinger Steer Vehicles). For more information about simple trailers see Simple trailer.

A heavy semi-trailer must have a rear axle set consisting of either:

  • a single axle set, or
  • a tandem axle set, or
  • a tri-axle set, or
  • a quad-axle set, provided the rearmost axle and the first or third axle in this set are steering axles and the semi-trailer does not form part of an A-train or B-train combination.

Gross mass

The gross mass of a semi-trailer (including its load) is the mass transferred to the ground through the axle(s) of that trailer. Any transferred weight from a following attached trailer is to be included in the calculation of gross mass of the first trailer.

The maximum gross mass of a rigid vehicle and one semi-trailer is 39 tonnes, unless it has at least two motor-driven axles in the rear set of the rigid vehicle.

Overall Length

The maximum overall length for a rigid vehicle and semi-trailer combination (including load, but excluding collapsible mirrors) is 19 metres.

Forward distance

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

Rear overhang

The maximum rear overhang for a heavy semi-trailer is 4 metres or 50 percent of the forward distance, whichever is less. The maximum for a light semi-trailer is 4.3 metres.

Front overhang

For semi-trailers, front overhang means the distance from the centre of the kingpin to the foremost point of the vehicle (including its load). The maximum is 2.04 metres radius arc ahead of the kingpin.

Towing two trailers (A-trains and B-trains)

A heavy rigid vehicle towing two trailers must be:

  • an A-train (a rigid vehicle connected to a semi-trailer that tows a full trailer), or
A-train

A-train

  • a B-train (a rigid vehicle attached to two semi-trailers connected at two points of articulation, where the forward distance of the longer trailer divided by the forward distance of the shorter trailer does not exceed 1.4), or
B-train

B-train

  • a heavy rigid vehicle followed by any combination of two trailers (not an A-train or a B-train), provided the trailer at the rear of the combination has a gross vehicle mass (GVM) that isn't over 3.5 tonnes and the gross mass of the combination is less than 20 tonnes.

Note: a light rigid vehicle (for example, a car or ute with a GVM of up to 3.5 tonnes) may only tow one trailer. Light tractors, however, are allowed to tow two trailers at a speed not greater than 50km/h.

Axles

For an A-train, the rigid vehicle must have at least two motor-driven axles in its rear axle set. A-trains and B-trains must not have retractable or rear-steering axles.

Tow coupling

For a B-train, the rearmost semi-trailer must not be coupled further rearward than the rearmost axle of the lead semi-trailer.

The coupling point distance for an A-train is the distance between the rear axis of the semi-trailer and the centre of the tow coupling connecting the full trailer to the semi-trailer. The maximum allowed is 30 percent of the forward distance of the semi-trailer.

Overall length

The maximum overall length for a heavy rigid vehicle towing two trailers (including load, but excluding collapsible mirrors) is 20 metres.

Simple trailers

Simple-trailer

Simple-trailer

A simple trailer is a trailer that has one axle set, and is not a semi-trailer.

A simple trailer is attached to the towing vehicle at a position well behind the position specified for a semi-trailer. Stinger Steer Transporters are simple trailer combination vehicles.

Gross mass

The gross mass of a simple trailer (including its load) is the mass transferred to the ground through the axle(s) of that trailer. Any transferred weight from the following trailer is to be included in the calculation of the gross mass of the first trailer. The gross mass of a combined rigid vehicle must not exceed 32 tonnes.

Axles

A heavy simple trailer must have an axle set consisting of:

  • a single axle set, or
  • a tandem axle set, or
  • a tri-axle set.

Overall length

The maximum overall length for a simple trailer (including drawbar and load) is 12.5 metres. The maximum overall length for a rigid vehicle and simple trailer combination (including load, but excluding collapsible mirrors) is 22 metres.

Forward distance

For a simple trailer, forward distance means the distance from the rear axis to the centre of the point of attachment of the towing vehicle. The maximum is 8.5 metres.

Rear overhang

Rear overhang means the distance from the rear axis to the rear of the vehicle or its load, whichever is greater. The maximum rear overhang for a heavy simple trailer is 4 metres or 50 percent of the forward distance, whichever is less.

For a light simple trailer, the maximum rear overhang is 4 metres.

Front overhang

For simple trailers, front overhang means the distance from the centre of the tow coupling to the foremost point of the vehicle (including its load). The maximum is 2.04 metres radius arc ahead of the tow coupling.

Tow coupling

For a rigid vehicle towing a heavy simple trailer, the tow coupling position must be at least 700 millimetres behind the rear axis of the rigid vehicle and not more than a distance equal to 50 percent of the wheelbase of that vehicle. The wheelbase is measured from the rear axis of the rigid vehicle to the foremost axle of that vehicle.

Note: for Stinger Steer Transporters, 'tow coupling' includes an articulated fifth wheel attachment with kingpin, or a ball attachment.

Inter-vehicle spacing

There is no minimum inter-vehicle spacing for simple trailers. The trailer (or its load) may overhang the towing vehicle.

Important

Drivers of vehicles that tow simple trailers (those with one axle set that aren't semi-trailers) also need to be aware that the simple trailer can impose a large weight on the rear of the towing vehicle that can (by lever action through the chassis of the vehicle) reduce the effective mass bearing on the front axle(s) of the towing vehicle. Simple trailers therefore need to be loaded carefully so that their load is distributed centrally over the axle(s) of the trailer. This will allow the towing vehicle to maintain front wheel traction.

Note: loading on a simple trailer is critical, as there needs to be a small downward force on the tow coupling to make sure a simple trailer remains stable while it's being towed.

Pole trailers

Pole trailers

Pole trailers

A pole trailer is a trailer attached to a towing vehicle by a telescoping or sliding pole, which is designed to support a common long load spanning between the trailer and the towing vehicle.

Overall length

The maximum overall length for a pole trailer is 11.5 metres (drawbar fully extended, but excluding the load). The maximum overall length for a rigid vehicle and pole trailer combination (including load, but excluding collapsible mirrors) is 20 metres.

Front overhang

Front overhang for pole trailers is the distance from the centre of the turntable on the towing vehicle to the foremost point of the load. The maximum is 2.04 metres radius arc ahead of the turntable centre on the towing vehicle (that is, the load on the trailer may hang forward of the turntable centre on the towing vehicle by this distance).

Gross mass

The maximum gross mass of a rigid vehicle and the pole trailer combination is 39 tonnes, unless the towing vehicle has at least two motor-driven axles in its rear axle set.

Pole trailers with one axle set

A heavy pole trailer with one axle set must have an axle set consisting of:

  • a single axle set, or
  • a tandem axle set, or
  • a tri-axle set.

For a pole trailer with one axle set, forward distance means the distance (excluding load) from the rear axis of the trailer to the centre of the point of attachment to the towing vehicle. The maximum distance is 8.5 metres, measured with the drawbar at full extension.

Rear overhang is the distance from the rear axis to the rear of the vehicle or its load, whichever is greater. The maximum rear overhang for a heavy pole trailer with one axle set is either 4 metres or 50 percent of the forward distance of that trailer, whichever is lesser. The maximum rear overhang for a light pole trailer with one axle set is 4 metres.

Pole trailers with two axle sets

A heavy pole trailer with two axle sets must have a front axle set consisting of either:

  • a single axle set, or
  • a tandem axle set.

A heavy pole trailer with two axle sets must have a rear axle set consisting of:

  • a single axle set, or
  • a tandem axle set, or
  • a tri-axle set, which is only permitted if the front axle set is a tandem axle set.

For a pole trailer with two axle sets, forward distance means the distance (excluding load) from the front axis of the trailer to the centre of the point of attachment to the towing vehicle. The maximum is 8.5 metres, measured with the drawbar at full extension.

For a pole trailer with two axle sets, rear overhang is the distance from the rear axis to the rear of the vehicle or its load, whichever is greater. The maximum for a heavy pole trailer with two axle sets is either 4 metres or 50 percent of the wheelbase of the trailer (where the wheelbase is measured from the rear axis to the centre point of the front axle set), whichever is lesser. The maximum for a light pole trailer with two axle sets is 4 metres.

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Last updated: 22 July 2014