Is a PBS combination right for you?

As defined by National Heavy Vehicle Regulator (NHVR) the Performance-Based Standards scheme is defined like this: “The Performance-Based Standards (PBS) Scheme offers the heavy vehicle industry the potential to achieve higher productivity and safety through innovative and optimised vehicle design.

“PBS vehicles are designed to perform their tasks as productively, safely and sustainably as possible, and to operate on networks that are appropriate for their level of performance.

“The basic principle of PBS is matching the right vehicles to the right tasks.

“PBS vehicles are tested against 16 stringent safety standards and four infrastructure standards to ensure they fit the existing road network and are safe.”

That last paragraph gives many operators the impression that PBS approvals are given only to brand new vehicles that boast the latest safety technology, but that’s not the case. Many PBS vehicles are quite old, but still manage to meet the regulations.

The jury is still out on whether that’s a good thing.

The attraction of a PBS combination is obvious. You get increased cubic capacity, improved productivity and freight efficiency, innovative and optimised vehicle designs for specific applications, and more flexible design and improved safety.

Critical parts of that design are making the truck and trailer combination perform safely on that route, while carrying larger payloads and having possibly longer overall length.

Factors including acceleration, braking, roll stability, trailer cut-in and tail swing are considered, before a PBS truck-and-trailer combination is approved for use on a designated route, approved by road authorities.

Common PBS combinations are shown in this NHVR configuration chart, but there are other combinations possible. More than a quarter of new heavy truck/trailer registrations are now PBS vehicles.

Trucksales’ research into the PBS question shows that there are several possible approaches to making PBS decision, but the optimum starting point may be with a reputable trailer maker that has extensive PBS experience, or with a PBS assessor.

These companies have to be up to date with the latest PBS dictates from the NHVR and from state and territory legislators, so they can advise on the best-fit combination for your freight task.

As an example, trailer maker MaxiTRANS has the following procedural recommendations.

Step one for operators is to consult with a dealer, to discuss what they wish to achieve, specifying products, routes and designated prime movers.

From that discussion, a preliminary concept will emerge and be converted into a concept drawing by MaxiTRANS Engineering.

Operators then approach their relevant road authorities, using the concept drawings, seeking ‘in principle’ approval. In cases where similar combinations have been granted PBS approval this step won’t be necessary.

Once the concept has been finalised, MaxiTRANS quotes the price and the cost of obtaining PBS approval.

With the order in hand, MaxiTRANS designs and builds the PBS trailer(s), liaising with NHVR for approvals.

MaxiTRANS says it arranges for inspection and certification of the completed prime mover and trailer combination by a PBS assessor, who provides the documentation necessary to secure a PBS permit.

A PBS approval covers the entire combination. This includes the prime mover and trailer(s) along with their as-supplied specifications. An example of that original specification is tyre size, speed and load ratings.

In August 2021, the NHVR announced it would allow a broader range of tyres; a move welcomed by chairman of the Australian Tyre Industry Council, Silvio de Denaro, as well as by PBS vehicle makers and operators. However, as at early 2022, replacement tyre choices are still quite restrictive.

Any changes or additions to a PBS combination must comply with PBS documentation as inspected by a PBS certifier, or the combination will require a new or amended PBS approval.

An example of that is where self-steering axles are digitally speed-rated and the trailer maker or operator increases that speed setting over the originally approved setting.

Other easily changed factors are trailer king pin and prime mover fifth wheel positioning, but these must not be varied from the originally-approved dimensions.

Some PBS approvals are for a specific route only, while others are for certain networks and that depends on the type of PBS units proposed.

It’s possible to get approval for a different make of prime mover on a PBS approval, giving operators more flexibility, but there will be certain mandated commonalities, including the type of drive-tandem suspension.

Opting for a PBS combination isn’t a cheap exercise and it needs to deliver exactly what the operator has planned. Help in ensuring that is available from PBS assessors and some are more helpful at the enquiry stage than others.

Oddly named Tiger Spider is a PBS assessor company that has a wealth of free info on its website tigerspider.com.au or (03) 9537 1027.

Insights on the website include a prediction that Victoria will remain the most progressive and supportive state for PBS vehicles and will soon allow access to up to one-third of their network to 36.5m (PBS L3A) combinations.

Tiger Spider can potentially see a significant shift away from A-Doubles to more innovative combinations in SA and NSW. A-Doubles are commonly seen now on major routes, hauling 40’ containers, but Trucksales notes that Super-B-Doubles with quad-quad axle groups have been successfully hauling two 40’ containers at around 110 tonnes GCM in various locations around the country.

The concept of multiple axles in groups is hardly new. Road authorities all around the world determine what axle weights they will permit, in the interests of pavement durability and bridge security.

In Europe, for example, single-drive axle loads up to 13 tonnes are permitted, while in the USA and Australia a drive tandem is needed to spread that much weight. Tri-axle groups with single tyres can carry 20+ tonnes in Europe, but in Australia duals are required to spread that load over a larger contact patch.

Possibly the most bizarre application of the multi-axle rule is in Michigan, USA, where eight-axle combinations of single or double trailers behind three-axle prime movers can carry up to 74.5 tonnes (164,000lb).

Of course, such leviathans aren’t permitted on the federally-funded Interstate road network, where the GCM limit remains 36.5 tonnes (80,000lb) on five-axle semi-trailer combinations.

There’s method in this apparent madness, according to research conducted by the American Association of State Highway and Transportation Officials and the Michigan Department of Transportation (MDOT). This research concluded that pavement damage is directly related to axle loadings, not gross vehicle weight.

In comparison with the Federally-approved, five-axle 36.5-tonner a Michigan eleven-axle, 74.5-tonne combo puts less load onto the pavement. The Interstater has typical dual-tyre-axle loads around 7.7 tonnes and the Michigan mobster imposes only a shade over six tonnes.

Most of the North American highway network is concrete, so the issue of tyre scrub as eleven axles make it around a corner is probably not so critical as it would be in a bitumen/substrate road environment!
We’re not likely to see eleven-axle, non-road-train combinations in Australia, but we’ll certainly see more quad-axle PBS combinations.

Very restrictive 'blueprint’ designs for quad-axle semi-trailer and B-Double combinations were PBS-approved some years ago and operators can use them to specify combinations that have access on PBS networks.

Vehicle requirements include: dual tyres on quad-axle groups; a steerable rear axle with at least +/- 12 degrees steering articulation and an effective centering mechanism; a load-sharing system at least as effective as for a tri-axle group and road-friendly certified suspension. Lift axles complying with ADR 43/04 are optional.

A steerable trailing axle means almost no more tyre scrub when a quad group is turning and, because axle loadings are slightly less in the three non-steerable axles than they are in a conventional tri-axle group, pavement damage isn’t increased over that caused by a tri-axle.