Truck Owner FAQ

  1. Terminology
  2. What is an axle group?

  3. What are the regulated dimension limits?

  4. What are the regulation mass limits?

  5. What is a road train?

  6. What is a turntable/fifth wheel?

  7. What is a semi-trailer?

  8. What is a converter dolly?

  9. What is a pig trailer?

  10. What is a dog trailer?

  11. What is a B-double?

  12. What is a block truck?

  13. What is a trailer drawbar?

  14. Who can I contact for more information?

 

1. Terminology

  • GCM: Gross Combination Mass
  • GVM: Gross Vehicle Mass
  • GTM: Gross Trailer Mass

 

2. What is an axle group?

  • Is a single axle group, tandem (bogie) axle group, twinsteer axle group, tri-axle group or a quad axle group
  • Different axle groups have certain requirements in relation to minimum and maximum axle spacings
  • Definitions for each type of axle groups are located in the Road Traffic (Vehicle Standards) Regulations 2002.

 

3. What are the regulation dimension limits?

Vehicles can be built to or carry loads to various dimensions, which are outlined in the following:

 

4. What are the regulation mass limits?

     

     Axles and Tyres
    Maximum axle group load

    Single Steer
    2 Tyres

    6.0 tonne

    Twin steer axle group
    4 tyres

    10.0 tonne for non load sharing suspension
    11.0 tonne for load sharing suspension

    Single axle
    4 tyres

    9.0 tonne

    Tandem axle group
    Dual tyres (8)

    16.5 tonne

    Tri-axle group
    Dual tyres (12)

    20.0 tonne
    18.0 tonne fitted to a pig trailer

     

    Vehicles must not exceed any manufacturer's limit.  The least value should be noted for components such as:

    • tyre rating;
    • axle rating;
    • gross vehicle mass (GVM);
    • gross trailer mass (GTM); and
    • gross combination mass (GCM).

     

    5.  What is a road train?

    A combination, except a B-Double, consisting of a motor-vehicle towing at least two trailers (counting as a single trailer a converter dolly supporting a semi-trailer).

     

    6. What is a turntable/fifth wheel?

    A device (except the upper rotating element and the king pin, which are parts of a semi trailer) used with a prime mover semi-trailer, or converter dolly.

    • The device allows quick coupling and uncoupling and provides for articulation.
    • A turntable is a load-bearing plate that supports vertical and horizontal loads, and is coupled to the semi-trailer's kingpin and locked into place by a set of jaws.

     

    Turntable/fifth wheel

     

    7. What is a semi-trailer?

    • A load carrying trailer that has its axle group towards the rear of the trailer.
    • A semi-trailer's forward connection is by means of a kingpin to either a prime-mover, converter dolly or lead semi-trailer. This arrangement allows up to half of the trailer's load to be carried by the prime-mover/convertor dolly/lead semi-trailer.

     

     Semi-trailer                             Road train with two (2) semi-trailers and one (1) converter dolly

            

     

    8. What is a converter dolly?

    • A short trailer with its forward connection by a drawbar. The drawbar normally pivots vertically.
    • Dollys are only equipped with a turntable.
    • Dollys are designed to carry some of the load of an attached semi-trailer rather than a load itself.
    • Road trains are an example of where a converter dolly is used as part of the combination.

     

     Converter dolly

     

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    9. What is a pig trailer?

    • A load carrying trailer that has an axle group near its centre.
    • Forward connection is by a drawbar, which is normally rigid.

     

    Pig trailer                                                            Rigid truck and pig trailer combination

                           

     

    10. What is a dog trailer?

    • A combination consisting of a fixed or converter dolly attached to a semi-trailer.

     

     Dog trailer                                                     Triple road train with 2 dog trailers

                 

     

    11. What is a B-double?

    • A prime-mover towing two semi-trailers.
    • The first trailer is a lead semi-trailer (A trailer), the second is a conventional semi-trailer (B trailer).
    • The lead semi-trailer (A trailer) has a turntable at its rear, which means another semi-trailer can connect without the use of a converter dolly.
    • B-triple are variations of this concept where three semi-trailers are connected.

     

     Lead semi trailer                                              B-double

                             

     

     

    12. What is a block truck?

    • A haul unit designed to tow other vehicles by means of a drawbar (rather than using a turntable).
    • They are often used to tow platforms, or a dog trailer, in situations where road trains are required to break up (split) at assembly areas.

     

    Block truck

     

     

    13. What is a trailer drawbar and it's length requirements?

    • Can be either a single rigid bar or an a-frame which is part of a trailer (except a semi-trailer) connecting the trailer body to a coupling for towing purposes.
    • The distance between the coupling pivot point on the drawbar of a dog trailer, and the centre of the front axle group or of the front single axle of the trailer, must not be:
      • over 5 metres; and
      • under 3 metres, if the trailer is used in a road train over 19m long.
    • The distance between the coupling pivot point on a drawbar, and the centre of the axle group or single axle on a trailer with only one axle group or single axle (except a semi-trailer), must not be over 8.5 metres.

     

    Drawbar

     

     

     

    14. Who can I contact for more information?

    Heavy Vehicle Operations

    Phone: 138 HVO
    E-mail: hvo@mainroads.wa.gov.au
    Fax: (08) 9475 8455

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Modified: 31 Oct 2013