The Tech's files #3 - Under pressure: regulated axle load limits

The sheer volume of industry and stakeholder discussions on zero-emission trucks is overwhelming, yet one clear theme is emerging – current axle load limits may completely strangle efforts to decarbonise the industry if not addressed.

Put simply, the heavy road freight transport industry will not be able to contribute to Australia’s mandated emissions reductions targets under the current axle load regulatory limits.

This edition of ‘The Tech’s Files’ looks at the interface between road and transport technology to unpack how we’ve ended up in this position, and explores options for what urgently needs to be done to address it.

Australia’s unique roads and trucks

Australia is a unique country. We have many unique truck and trailer combinations that simply don’t exist anywhere else in the world. The fact that we’ve pushed the boundaries in truck and trailer size, gross mass, and configuration is well known, but you may not be aware that decades ago, Australia also broke new ground in terms of the roads they drive on as well.

Unlike many other developed countries, much of Australia is thinly populated and features incredible distances between its populated areas, both small and large. This creates an infrastructure challenge – how to provide an expansive yet reliable network of sealed roads suitable for both light and heavy transport. An innovative, cost-effective road structure type known as the ‘sprayed seal’ turned out to be the solution.

Sprayed seals and load limits

Sprayed seals are an interesting departure from the other road structure designs. They are effectively a thin layer of bitumen that is sprayed as a hot liquid onto a compacted base layer (i.e. dirt and/or crushed rock), which is then covered with a layer of aggregate (i.e. small stones of the same size and shape), which forms the road surface itself.

Often, the base layer underneath the bitumen is ‘unbound’ which means that it may be treated with a stabilising agent such as cement, but sometimes is not treated at all.

The end result is a relatively cheap and easy to construct flexible road type that is suitable for roads carrying several thousand vehicles per day.

Usage of sprayed seals grew rapidly after their introduction in the early twentieth century, and they now account for around 70% of the total length of all sealed roads in Australia.

Yet within the advantages of sprayed seals also lie their weakness – being very thin, they are susceptible to increases in applied load, unlike other structure types.

While there are other factors, this is largely the reason why axle load limits are lower in Australia than other developed countries, where rigid road types such as asphalt and concrete that are thicker and more robust tend to predominate.

Bad news for zero emission trucks

This is bad news for zero emission trucks in Australia. They are likely to have higher tare (i.e. unladen) weights than conventional internal combustion engine trucks, due to the equipment comprising the electric drivetrain.

For Battery Electric Vehicles (BEVs), the extra weight is in the battery and the electric motor. For hydrogen Fuel Cell Electric Vehicles (FCEVs), the weight of the fuel cell and the hydrogen storage and delivery system is also added on top of the electric battery and motor.

In both cases, the result of removing the internal combustion engine, its ancillary hardware, and the diesel fuel tanks, and replacing them with either the BEV or FCEV hardware is a significant net mass increase. This increase cannot be abated in any other way, nor can it be ‘engineered out’ within the constraints of current technology.

Pushing the boundaries

While spray seal roads make up 70% of the sealed road network they tend to be most common in remote and low traffic areas. Much of the urban network and many of the major rural roads have stronger, thicker top layers, and bound sub layers, and are better suited to higher loads. Not only do these roads account for most of the freight task (in terms of tonne-km), they also more frequently upgraded, and are more likely to have the charging/fueling infrastructure to support BEVs and FCEVs. It is critical that we don’t allow the load limitations of spray seals get in the way of the roll out of zero emission technologies.

Driving forward

Australia’s heavy road freight transport industry will not be able to contribute to the necessary reductions in greenhouse gas emissions under the current axle load limits framework.

Worse still, it is on a path to becoming the highest emitting industry in Australia if nothing is done. So what needs to happen?

Action 1 – Classify roads based on road structure type, strength, and durability

• Classification of roads by structure type is not only sensible and technically feasible, it is supported by precedents.
• Australia already sets the international benchmark for assessing and classifying vehicles according to their performance standards.
• Roads are already assessed in terms of geometry, and bridges are assessed for strength.
• Assessment and classification of road structures that match the higher axle load demands of zero emission trucks is the next logical step.

Action 2 – Develop public network access maps showing roads suitable for zero emission trucks

• The online platforms for displaying heavy vehicle route access already exist at the state and federal government levels.
• Roads likely to be needed by zero emissions trucks will tend to be higher-standard roads in metropolitan and urban areas.

Action 3 – Utilise telematics for assurance of road/route compliance

• The use of telematics for compliance assurance in relation to mass is also supported by precedents, in the form of on-board mass systems.
• Zero emission trucks fitted with telematics systems can assure regulators that the vehicles are only operating on assessed and approved roads.

Action 4 – Research into next generation sprayed seal pavements to support higher axle loads

• Australia was an early innovator for sprayed seals in the twentieth century
• Its time for government and researchers to repeat that exercise to identify solutions for roads that will meet the challenge of twenty-first century trucks.

It makes no sense to prevent the introduction of zero emissions vehicles on the basis of fears to damage or accelerated wear to road structures that they may not need to operate on.

Australia has been ‘sweating the road asset’ for many years in order to meet the productivity demands of the freight task.

It is time to refocus on the environmental demands, and sweat the asset from that perspective. Australia has the capability and technology to resolve this problem, and must urgently act to do so.