Regulatory Advice – Managing the risk of a light or empty lead trailer in a laden B-double

Note: This information is intended as general guidance only and does not constitute legal advice. We encourage you to obtain independent advice about your legal obligations. If you have any feedback on the information provided, please contact us at info@nhvr.gov.au

This regulatory advice provides guidance on managing the risks associated with a light or empty lead trailer in a laden B-double.

Image is of a b-double with an empty trailer.

Who is this advice for?

This regulatory advice provides guidance for:

Background

Feedback from industry is that when driving a laden B-double with a significant load imbalance between the axle mass on the lead trailer and the axle mass on the rear trailer, the vehicle ride quality is impacted significantly. Ride quality can be further impacted in undesirable driving conditions, such as wet weather, poor road condition or unfamiliar roads. Drivers have emphasised that ride quality is impacted to such an extent that there is a perceived vehicle instability, which is concerning for drivers operating heavy vehicles in these conditions.

A safety concern highlighted by industry in addition to the poor vehicle ride and behaviour is the effect a very light or empty lead trailer has on the vehicle’s braking performance when the rear trailer is fully loaded. In these circumstances, emergency braking, braking on wet roads, and even the use of compression brakes, can result in significantly increased braking distances or a loss of control of the vehicle. This risk is escalated if the driver is unaware of the load imbalance when they begin their journey.

Load imbalance impacts on a vehicle’s traction and ability to maintain forward motion while going uphill. The impacts of ride quality can cause driver stress and lead to driver distraction and/or premature fatigue. It is well known that fatigue can impair a driver’s ability to maintain proper control of a heavy vehicle. Fatigue reduces alertness, slows reaction times, and increases the likelihood of a heavy vehicle driver being involved in a crash.

Why is this important to my business?

To ensure the safety of transport activities, CoR parties should implement suitable scheduling, loading and unloading plans to ensure acceptable load balance is maintained by reducing the likelihood of a significantly light or empty lead trailer. When scheduling the loading and progressive unloading of B-doubles, load distribution should also be considered, as it helps maintain ride quality.

What are my legal obligations?

Parties in the Chain of Responsibility

Parties in the CoR have a duty under the Heavy Vehicle National Law to minimise the risk of their transport activities.

Under the HVNL section 26C, each party in the CoR has a Primary Duty to ensure, so far as is reasonably practicable, the safety of the party’s transport activities relating to the heavy vehicle.

This is an obligation to eliminate or minimise public risks, and a prohibition against directly or indirectly causing or encouraging a driver or another person, including a party in the CoR, to contravene the HVNL. CoR parties and their executives, should be aware that they remain a CoR party even when their transport activities are contracted, or subcontracted, to another party.

Under the HVNL section 26A, safety of transport activities relating to a heavy vehicle is the shared responsibility of each party in the CoR.

Under the HVNL section 26B more than one entity can concurrently have a Primary Duty for the same transport activity, and each duty holder must discharge that duty so far as reasonably practicable.

Under the HVNL section 26D, executives of a business that is a party in the CoR must exercise due diligence to ensure the business complies with its Primary Duty.

Note: Transport activities includes all activities and business processes associated with the use of a heavy vehicle on a road.

What are the legal consequences?

If your business is a party in the CoR and it fails to eliminate or minimise public risks so far as is reasonably practicable, then it may be in breach of its Primary Duty. If a breach is proven, the law provides sanctions against a company and its executives, ranging from education and formal warnings for minor offences to improvement notices and prosecution for more serious offences.

What are the hazards and risks?

Hazards associated with load imbalance between the front and rear trailer on a B-double may include:

  • reduced brake performance in wet conditions or heavy braking events that increase the risk of loss of control or potential jack knife
  • mechanical failure due to increased wear and tear
  • increased driver fatigue and distraction due to ride quality and uncomfortable vehicle behaviour
  • impacts to driver stress and mental health.

The potential safety risks resulting from these hazards may include:

  • serious or fatal injury to heavy vehicle drivers and other road users
  • damage to public and private infrastructure.

Why is it important to manage the hazards and risks?

By appropriately managing these hazards and safety risks, CoR parties can:

  • prevent serious and fatal injuries to heavy vehicle drivers and other road users
  • reduce fatigue and distraction events
  • improve vehicle behaviour, which will help reduce driver fatigue and distraction
  • reduce wear and tear on the vehicle or trailer
  • create a safety culture in their business where heavy vehicle drivers are encouraged to make informed decisions about safety
  • enhance a business’s reputation, and position it as a business or employer of choice.

How do I manage the risks?

One of the most effective ways for CoR parties in the heavy vehicle supply chain to manage the safety of their transport activities is to adopt and actively use a Safety Management System (SMS) as part of their everyday business.

An SMS is a systematic approach to managing safety which, once implemented, will help CoR parties identify how to ensure the safety of their transport activities, so far as is reasonably practicable.

As part of the risk management process, CoR parties should:

  • identify hazards associated with their transport activities
  • assess the risks associated with those hazards
  • identify and implement control measures to eliminate or minimise those risks
  • review the effectiveness of control measures, either periodically or after any incident, to ensure they remain effective.

As a party in the CoR, you may consider specific control measures, such as:

  • implementing a feedback channel to enable employees, including drivers, to provide feedback or raise their concerns and ensure a considered response is provided
  • implementing appropriate scheduling, loading and unloading practices to ensure the safety of your heavy vehicle transport activities. The Load Restraint Guide 2025 provides guidance and practical advice on how to meet loading requirements and loading performance standards
  • developing and implementing policies and procedures to eliminate or minimise the likelihood of load imbalance and the flow-on effects on drivers
  • implementing loading plans
  • providing information to drivers on critical load information prior to starting their journey
  • promoting a culture of safety in your business.

Note: Good practice, which is supported by desktop modelling, is to ensure that the mass on the drive axle group is at least 20% of the total combination mass. For example, for a B-double loaded at 62.5t total combination mass, 12.5t is required on the drive axle group (62.5 x 0.2 = 12.5). This does not apply to an unladen vehicle. 

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