In this edition of ‘The Tech’s Files’, HVIA’s monthly series that explores topical technical issues impacting the trucking industry, we’re looking at the possibility of technology transforming the future of the NHVR’s Performance Based Standards (PBS).
Why PBS, why technology, and why now? PBS is old news, surely….it’s been around for more than 20 years! If it was going to be transformed by technology, wouldn’t that have already happened?
That’s only partially correct. PBS is indeed old – it began in 1999 as an arrangement between the National Transport Commission (NTC), the Australian Road Research Board (ARRB), Austroads, and the federal and state transport agencies.
The following years saw the necessary research, reporting, and regulatory revisions, before the scheme officially commenced in 2007 under the NTC, before being transferred to the NHVR in 2014.
Since the inception of PBS, technology hasn’t featured particularly prominently. Most of the advances and benefits have been delivered through innovative vehicle geometric design, such as adding extra axles to rigid trucks and dog trailers, shortening A-doubles, and lengthening B-doubles.
What we’ve been missing is the spark to jump-start clever technological solutions to address the ongoing constraints. But that spark may have just started glowing – the NHVR recently released a discussion paper on the future of PBS which proposed 15 specific questions intended to guide its future direction to ‘PBS 2.0’. Crucially, it included the following suggestion regarding technology:
“The NHVR suggests the adoption of interim standards to temporarily enable field testing of technology not already in the PBS scheme. What are your thoughts on the soundness of this concept and how interim standards could potentially be developed?”
If implemented, this suggestion could see the creation of a range of innovative standards that allow future PBS vehicles to use technology to go above the current mass and dimension limitations in exciting ways.
So let’s have a look at three ways current technology can be used to transform the future of PBS
(Disclaimer: Do not try any of these ideas at home. The technical feasibility varies widely, and they may not be practical or sensible).
Dynamic loading
Even though the premise of the NHVR’s PBS is that it allows vehicles to exceed certain regulatory-imposed barriers, one of its untouchable tenets is that the existing axle mass limits cannot be exceeded. It requires that all vehicles conform to the Heavy Vehicle National Law (HVNL) Mass and Dimension Limits for axles and axle groups.
Why does such a limitation exist in PBS? There is an important reason – to limit the impact of the vehicle’s weight on the structure of the roads and any bridges it crosses. These aspects are the domain of asset management engineers, who advise us that breaching axle load limits can have serious consequences for the lifespan of road and bridge infrastructure.
All roads and bridges are designed using various assumptions about trucking operations, including how heavy the vehicles are when being operated. To be prudent, these assumptions are conservative and allow some margin for error.
If they did not, the lifespan of the infrastructure could be much shorter than intended, but it is within those conservative assumptions that an opportunity for a technical solution lies.
If it could be demonstrated that a vehicle’s impact was lower on the road than predicted by the desktop analysis applied to it, it would justify increasing the allowable mass carried (possibly above the HVNL limits), as the overall impact on the infrastructure would be no worse.
One way to do that is by measuring and reporting on the vehicle’s dynamic loading. Dynamic loading is a measure of the actual, ‘real-time’ forces imposed on a road surface while a vehicle is in motion. When a vehicle is heavier, the force is greater. When a vehicle travels over a bump, the force momentarily increases as the vehicle bounces on its suspension, before falling back to its normal level.
In practice, accurate measurements of dynamic load are quite difficult to achieve, but a high level of precision is not necessary. All that is needed is an estimate of dynamic load, and that is possible using technologies already available, and in many cases, already fitted to vehicles.
PBS vehicles are routinely specified with advanced electronic braking systems, and tyre pressure monitoring. These systems include the necessary sensor technologies to measure air suspension airbag pressure and tyre inflation pressure, two parameters that could be used to estimate dynamic loads during operation.
The necessary next steps are a research project to develop and validate a dynamic load model using the airbag and tyre pressure data, and its inclusion into the vehicle’s electronic braking system software as a monitored and recorded parameter.
Offset tyres
Sticking with the topic of impacts on roads, there may be another unique opportunity to use technology to limit road wear/damage, and possibly also allow for axle mass increases.
One of the principal concerns of road managers is that heavy vehicles and their trailers can damage roads by generating ‘ruts’ over time.
While the causes of rutting are not limited to vehicles, the situation is not helped by the fact that the distance along an axle between the tyres (also known as ‘track width’) is usually maximised to aid stability, and does not typically vary much between manufacturers. This leads to a concentration of the forces applied by trucks in the outer edges of the lanes.
But what about loads where stability is not a concern, such as low volume, high mass, and high-density loads such as steel, and bulk industrial goods and materials?
Vehicles carrying those loads tend to have a low centre of gravity, which corresponds to a high rollover threshold, and excellent resistance to rollover.
For those vehicles, narrowing the track width of one of the axles may not degrade stability to an unsafe level. This leads us to the concept of ‘offset’ tyres on one axle in an axle group as a means of limiting impacts on pavements, and potentially allowing an axle load limit increase.
Sliding axles
The impact of vehicles on bridges has been one of the enduring limitations of PBS, and is usually at the heart of issues related to access and productivity.
An important trade-off comes into play – shortening vehicle overall length improves manoeuvrability, but ‘concentrates’ the vehicle’s weight into a smaller space, increasing its impact on bridges.
The only way to alleviate this is to lengthen the vehicle’s overall dimensions and increase the spread between its axles to better distribute the weight, which comes at the cost of reduced manoeuvrability.
Sliding axles could potentially address this issue.
A vehicle’s axle positions and the distance between individual axles in a group could be adjusted to best suit the geometry of the bridges that it encounters. The axles could sit within a hydraulically-actuated sliding subframe mounted to the trailer chassis, and operated by the driver from the cabin, or from outside the vehicle.
Similar technical solutions already exist within the market – some trailers feature hydraulically sliding decks to accommodate wide loads, and some trailers extend this to hydraulically sliding frames, that feature individual axle ‘modules’.
Will electronically monitored, offset tyres on sliding axles become a reality under PBS 2.0? Maybe not, but it’s a safe bet that the industry will propose other exciting options if the NHVR opens the door to interim standards and field trials.
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