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A-double: A PBS success story


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Prime Mover Magazine  /  March 21, 2019

Can the A-double change the trucking industry? That was the question posed at the start of a very comprehensive story back in 2011 on the then fledgling A-double combination.

Now eight years down the track, it would appear the answer is a resounding yes.

When the concept of Performance-Based Standards (PBS) was first mooted more than two decades ago, the visionaries of the scheme had general ideas of the kinds of innovative vehicles that could be nurtured.

The main thrust of PBS, as it transpired, was to create a space for innovative designs capable of enabling a quantum leap in productivity improvements for transport on Australian roads.

In the earlier years following the turn of the century (the PBS scheme was introduced in 2007) most of the PBS approvals on the highway achieved small productivity gains due to incremental dimension changes, extra axles or self-steering axles.

Enter the A-double.

Finally, in 2010 a combination emerged with the potential to make the quantum shift required to give PBS some credibility, providing the sort of productivity boost for which the industry had been crying out.

Ironically, the A-double is probably the simplest of all the combinations, comprising two semi-trailers linked by a tandem-axle (there are A-double combinations with tri-axle dolly) converter dolly. But herein lies one of its greatest strengths – versatility – because it can be easily separated into two standard semi-trailers.

In the past, this combination – known logically enough as a double road-train – was seen as a necessary evil in remote areas, but on-road performance made it unsuitable to come anywhere near large centres of population or busy traffic conditions.

However, all that changed due to the inclusion of modern technology, specifically focussed on the converter dolly, as part of an intense engineering effort by a number of trailer manufacturers including Haulmark Trailers to get the A-double concept up and running.

“The whole thing started in late 2006 after Haulmark had been involved in the PBS process for many years,” says Haulmark’s National Sales and Marketing Manager, Mark Johnston. “We had built a number of PBS approved vehicles, steerable extendable trailers and a 52-foot trailer without a self-steering axle.

“The A-double is the game-changing solution which comes up with the very elusive quadruple bottom line: It offers considerable improvement in productivity, emissions, congestion and safety for everyone.”

Developing vehicles for PBS requires a deep understanding of how a vehicle performs. Designers need to know where it performs well and where it doesn’t perform well. They have to identify what needs to be worked on and improved to meet the standards.

Understanding the dynamics of these vehicles leads to developing the technology to provide solutions.

“We need to continually find solutions for the growing freight task, to control emissions, deal with congestion, all of those things,” Mark says. “We take the principles of PBS, our understanding of the dynamics of vehicles and then we try to apply technology to a range of those vehicles to see which is actually going to come up with the real trump card.

“We came up with the A-double concept because it gives us a significant step up in mass – up to 85 tonnes gross combination mass (GCM) – a significant step up in trailer length and in so doing we significantly improve emissions and congestion with a safer vehicle.”

Fast forward to the present and according to Mark Johnston, the success of the A-double between Toowoomba and the Port of Brisbane has been phenomenal and there are now more than 150 of these super-efficient combinations plying this route. He estimates that this equates to around 200 less trucks used for this purpose compared to before the A-double was introduced. However, he maintains the ongoing stumbling block to wider use of higher productivity PBS-approved combinations like A-doubles is the approval process.

“It requires a positive mind-set on the part of the road managers, be it state or local government, in wanting to make these things happen in a timely fashion so that operators can make a business case for investing in these vehicles,” Mark explains. “If this happens then it can actually make a big difference by removing a large number of trucks from a given route. This has the flow-on effect of improving safety, reducing greenhouse gas emissions and making things commercially more palatable for operators.”

Prime Mover also spoke with Les Bruzsa the Chief Engineer of the National Heavy Vehicle Regulator (NHVR), who reiterated that the original purpose for developing the A-double centred around carrying containers from Toowoomba to the Port of Brisbane.

He explains that the original A-doubles have an overall length of 30 metres and are able to carry two 40-foot containers and up to four 20-foot containers, depending on how much each weighs, providing 100 per cent productivity benefits for specific freight tasks like containers

For example, two 20-foot containers of grain weighing up to 30-32 tonnes each can be carried on the centre of the trailers for the inbound journey and four empties carried on the return trip, which is not possible on conventional combinations like B-double or prime mover semis.

“This combination is certainly one of the PBS success stories,” Les exclaims. 

Another is the four-, five- and six-axle truck and dog tipper combinations, with the quad-axle variants proving particularly popular.

He went on to say that last year the NHVR approved 1,862 PBS combinations which is around a 30 per cent increase on 2017.

“In general PBS is growing very quickly, we approved 197 PBS A-double combinations last year,” Les says.

While the A-double had its formative years in Queensland, other jurisdictions are also starting to realise the benefits.

“Now we have A-doubles operating in South Australia, NSW and Victoria while the first approval for Tasmania is due to happen soon.”    

Les suggests the willingness of road authorities to recognise the benefits of PBS combinations to the road network and society in general has markedly improved in recent times.

For example, he cites the development of A-double combinations with an overall length up to 34 metres which enables larger axle spacings between the axle groups leading to less strain on older bridges.

“The original 30 metre A-double is still probably the most common but we now have shorter and longer versions including 26 metre and up to 34 metre units which still meet Level 2 PBS requirements.

“We have some A-doubles operating in Victoria at longer than 30 metres because at the 30-metre limit they would have had too large an impact on certain bridges.”

In summing up, Les remarked that A-doubles represent a good option compared to B-doubles due to the extra axle group.

“This means a given load is distributed over more axles and a longer distance which reduces the impact on roads and bridges.”

As the momentum of PBS-approved vehicles increases and with further development of a ‘bigger picture’ approach to access approval by road regulators, it seems the use of high productivity combinations like the A-double will continue to grow.



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