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What is a B-Double?

B-Doubles are one of the most popular classes of heavy haulage trailer combinations seen on Australia’s roads every day, but while they’re often confused for road trains they are not the same thing.

Understanding B-Doubles vs. Road Trains

It combines a prime mover attached to two semi-trailers, linked together by a fifth wheel. It’s the fifth wheel that makes it distinct from a road train, as the wheel provides a level of extra stability. Additionally, there is a turntable present at the end of the lead semi, allowing it to connect to another semi without the need of a converter dolly, another step beyond the simpler design of the road train.

It’s estimated that there are over 10,000 B-doubles on the roads every day in Australia, and that number is set to rise even more every year as it’s one of the most popular combinations on the market.

They first came onto the scene in the early ‘80s in Western Australia and Victoria, with the concept proving so successful that it soon found nationwide approval. A decade later they were found all over the country after Tasmania finally granted approval to the model.

Length Specifications of B-Double Trucks

Since then the configuration has evolved to keep up with new technology and the unique demands of Australian roads. Among the changes were going to two tri-axle configurations and using that extra tri-axle to increase the overall length from 23 metres to 25. Mass limits slowly increased to 68 tonnes after trial periods.

According to the NHVR classification, B-Doubles are currently a class 2 heavy vehicle that can be up to 26 metres in length and can have seven, eight or nine axles.

Variations of the B-Double truck

There are many variations of the B-Double configuration specially designed for longer, heavier loads, including the A-Double, AB-Triple and even the Quad-Quad-Super B Double. O’Phee Trailers, part of The Drake Group, make the B-Double Combination with twist locks, and also the B Double combinations with lead sliding subframe and rear MkIII.

Contact The Drake Group today to see how our range of heavy haulage trailers is purpose-built for every scenario.

Image: Donmay Transport B-Double Lead Flattop
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