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A treatise by Martin Phippard

One of the most fascinating aspects of the trucking industry in Australia is the sheer number of permitted configurations. But because almost everyone both inside and outside the business of road transport tends to associate the country’s biggest trucks with Outback road trains there is a natural inclination for outsiders to describe almost any big combination as a ‘Road Train’.

Needless to say this is far from correct although it is only fair to add that even in Australia itself there exists an element of confusion when it comes to accurately describing certain vehicle groups. Indeed conversations with drivers and road transport officials confirm that terminology often varies from State to State and from industry to industry. So it is hardly surprising that it is often more expedient to make reference to any large, multi-trailer combination as a ‘road train’ regardless of the actual configuration. Purists, however, would beg to disagree!

In fact in Australia a road train in the literal sense is any two or three-trailer combination hooked together via dolly converters. Larger, more complex examples do exist of course, but these are generally confined to fairly remote regions and are seldom seen by the general motoring public.

Please note that this collection of information and photographs has been assembled for the purposes of introduction to truck terminology only and should not be regarded as the definitive work. Comments and observations are welcomed by the author.

Thanks are due to Rufus Carr, Gary Millewski, Tom O’Connor and Ron Knight (deceased) for the use of several photographs.


The concept of hauling two or more trailers thereby creating a train originated long ago in the 1920s when steam-driven locomotives hauled several trailers across the desolate regions of the Northern Territory. The idea took a significant leap forward in 1934 when the British manufacturer, AEC, delivered an 8x8 truck designed to pull two purpose-built four-axle trailers across uncharted regions North of Alice Springs. This combination was known simply as ‘The Government Road Train’ and in many ways served as a model for later designs. Its unique axle lay out incorporating steering axles at the front and rear of the truck and self-steering bogies on each of the trailers ensured that each wheel on the combination followed exactly the same path. This proved a blessing in areas where ‘roads’ were often simply rough, meandering tracks through the bush.

Kurt Johannsen Diamond T

The AEC road train worked in Australia for ten years and covered 800,000-miles. It was succeeded in the immediate post war years by larger, more powerful vehicles pioneered by trucking icons Kurt Johannsen and Dave Baldock. In 1947 these entrepreneurial bush engineers converted military surplus Diamond T 980 trucks and used them to pull as many as seven ex military or home-built trailers. Kurt Johannsen specialized in the movement of livestock while Dave Baldock opted for general freight. This era is generally associated with the birth of the ‘modern day’ road train.

Foden Road Train Rotinoff Road Train

Throughout the 1950s and ‘60s road trains, in various guises, continued to form the mainstay of long distance trucking operations in the Australian Outback. Trailers were usually flat decks, tankers or livestock crates.

Kalari Transport 3-trailer Road Train Kenworth 2-trailer Road Train Mack 2-trailer Road Train
Western Star 2-trailer Road Train Western Star 2-trailer Road Train Livestock Road Train
KW 3-Trailer Road train Mack 3-trailer Road train
Kenworth Road Train Mack Road Train

When legislation controlling overall length and weights was first introduced in the late 1960s this allowed for a maximum of three 40-foot semi-trailers to be pulled behind a 6x4 tractor unit or two trailers behind a rigid ‘body’ truck. Maximum weight was set at 115-tonnes provided that the combination rolled on a sufficient number of axles and overall length was 50-metres (165-feet).

In Western Australia, however, rigid trucks with twin-steer axles pulling three trailers could operate legally at weights of 137-tonnes, again with the provision that there were sufficient axles and wheels under the combination...

It was not until the 1980s that B-trains known as B-doubles were introduced to Australia (See B-Trains, Interlinks and B-Doubles) and 1991 before they were allowed to operate throughout the nation. Since that time the popularity of the B-double has increased enormously and the idea of linking two or more trailers using a fifth wheel rather than a dolly has been greatly expanded.


Argosy B-triple Neils Transport Air Road Kenworth B-Triple Bunker Freightlines Volvo FH B-Triple
Hahn Kenworth B-Triple tanks Kenworth B-Triple operated by Nascatrans
Argosy B-Triple in colours of 1st Express DHL B-Triple


The B-triple marks the obvious and most natural evolution of the B-double and is – as the name suggests – three trailers coupled to one another via fifth wheels.

This configuration is now widely used by parcel carriers utilising high volume curtain-sider trailers and is popular with companies operating on the 1,700-km Adelaide to Perth route. B-triple trailer sets have also been developed for livestock, tankers and for bulk materials.

B-triples may operate at lengths up to 36.5-metres (120-feet) overall and at weights of up to 86-tonnes, the same as a two-trailer road train featuring tri-axle groups throughout.

Hubbard Western Star AB Triple Western Star AB Triple


Another configuration that has gained wide acceptance with operators, particularly those engaged in bulk haulage, is the AB-triple.

This three-trailer combination is made up of a regular semi-trailer (the A-trailer) coupled via a dolly converter to a two-trailer B-double set. Axle groups may be tandems or tri-axle and this factor dictates the maximum gross weight of the combination. Again maximum overall length is 36.5-metres.

(No images available)

A three-trailer combination made up of a B-double coupled to a single A-trailer via a dolly converter. The reverse of an AB-Triple.

Giacci BB-Quad Giacci BB-Quad


This four-trailer combination comprises two B-doubles coupled together via a dolly converter. The configuration is used primarily by bulk operators employing tankers or side-tipping trailers. In Western Australia companies such as Giacci Bros employ this set-up behind four and five-axle tractor units (prime movers) and by using tri-axle groups throughout – including the tractor unit’s drive axles – can achieve gross weights approaching 150-tonnes.

Mitchell Fuel Kenworth 2AB Quad Mighty Atom 2AB Quad BP Volvo 2AB Quad


Adapted by inventive operators to comply with the current overall length limit of 53.5-metres (175-feet) and exploit tri-axle load limits of up to 23.5-tonnes, the 2AB Quad is a four-trailer combination made up of two A-trailers (regular semi-trailers) coupled via a dolly converter and, in turn, hooked up to a B-double set.

These combinations are extensively used by fuel giants Shell and BP on long-distance runs between Adelaide and Darwin and can gross approximately 194-tonnes when used in conjunction with a tri-drive tractor unit thereby employing eight tri-axle groups each capable of accommodating 23.5-tonnes.

There is some debate as to whether the two A-trailers should be at the front end of the combination – ahead of the B-double, at the rear end – behind it, or even at either end with the B-double sandwiched in between. It appears that operators have their own ideas as to which set-up handles best and enjoys the best road manners when running at the supposed legal maximum speed of 90-kph or 56-miles per hour.


Doug Gould 4-trailer Hampton's 5-trailer combination Cannington Icon 6-trailer combination

At this point much of the existing terminology becomes a little confused. Vehicles such as a B-double coupled to a B-triple via a dolly converter are found in some of the more remote regions of the country and the now internationally recognized Cannington ICONS are made up of a tri-drive Mack tractor unit pulling two B-triples hooked together by a tri-axle dolly converter. One can only assume that such combinations would be called ‘2 B-triples’ but it is probably fair to say that Doug Gould from Kalgoorlie summarised the situation well by stating that “Out here you can call it what you bloody well like!”

The ICONs are of particular interest because they have worked successfully for several years at weights of 194-tonnes (213-US tons) In addition the six trailers, built by Byrne, cleverly manage to incorporate eight side tipping bodies!

These combinations, together with the four trailer combinations operated by Doug Gould and Mitchell Bulk Services, are driven on State highways and have to comply with all State and Federal laws. The fact that they do conform and have worked without incident for several years testifies to the skill of the drivers and the sophisticated construction of the vehicles themselves.


Kenworth C-510 with B-Triple coupled to a B-double. Third trailer is powered independently. Burton Kenworth C-510 B-triple plus B-double
Twin engine five-trailer combination in Western Australia 250-Tonne off-highway Road Train
Gary Millewski Twin-engine Mack Pit Hauler Gary Millewski Twin-engine Kenworth Pit Hauler Yarrie Kenworth Twin Engine Pit Hauler

While most visitors to Australia will have encountered a road-going road train at some point and have marvelled at its size, few will have ventured far enough into the Outback to have come face to face with the seriously big kit working on private haul roads.

Again these vehicles defy any attempt to categorize them. They are found in many configurations ranging from fairly straightforward, if oversized two and three trailer road trains to truly remarkable five-trailer outfits powered by two engines!

The big problem encountered by heavy combinations required to work off-highway is one of traction and for this reason manufacturers such as Kenworth and - until recently – Mack produced oversize tractor units measuring 3-metres (10-feet) or more across the rear bogie. These units, working in conjunction with specially-built trailers measuring up to 3.6-metres (12-feet) wide were nominally rated at around 250-tonnes but often work at weights considerably in excess of this figure.

For weights in excess of 300-tonnes combinations employing a ‘powered trailer’ have been introduced in recent years and many are now working in Australia’s booming ore and coal mines.

Featuring an engine and automatic gearbox (transmission) driving to a tri-drive bogie utilising Finnish-built Sisu hub-reduction (planetary) rear ends the powered trailers may be installed at any point in the multi-trailer combination but is usually found somewhere near the middle. This power unit is used when the combinations - which can gross at weights approaching 500-tonnes (550-US tons) – are lifting off from a standing start or are required to negotiate an adverse gradient. The power is applied by the driver of the combination using a hand throttle in the cab of the prime mover. Six such combinations, owned and operated by Brambles Industrial services are currently at work in Northern Queensland hauling coal mined by Thiess Construction. Each of these outfits, made up of five trailers, measures an intimidating 69.25-metres (220-feet overall) and is capable of grossing 480-tonnes when fully freighted.

As the cost of fuel continues to rise and the value of raw materials increase, so ever more inventive ways of moving large volumes of freight will be introduced. However, there is no doubt that when it comes to new and inventive configurations, Australia’s road transport operators take first place!

*** ENDS ***

A special THANK YOU to Rufus Carr, Tom O'Connor, Gary Millewski and Ron Knight (deceased) for the use of some of these photos.

If anyone visiting this site has information which supports or contradicts this information or can help in any way with additional material,
please contact Hank Suderman. Thank you.