Managing risks of light or empty lead trailers in a laden B-double
Guidance for safely managing risks of light or empty lead trailers in a laden B-double is the focus of the latest regulatory advice to industry from the National Heavy Vehicle Regulator (NHVR).
The NHVR said feedback from industry and drivers highlights a critical safety concern when B-doubles are loaded unevenly, specifically when the lead trailer is light or empty and the rear trailer is heavily laden.
“This imbalance can significantly affect the vehicle’s ride quality, handling, and braking performance, particularly in wet or low-traction conditions,” the regulator said.
“Drivers have reported that these loading conditions can lead to instability, increased stopping distances, and reduced control, especially during emergency braking or cornering.”
The regulator also said 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.”
The NHVR also reminded industry that all parties in the chain of responsibility (CoR) have a duty under the Heavy Vehicle National Law to minimise the risk of their transport activities.
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 as part of their everyday business, the regulator added.
To ensure the safety of transport activities, the NHVR said 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.”
The regulator also noted that good practice, which is supported by desktop modelling, is to ensure that the mass on the drive axle group is at least 20 per cent 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.”
For more guidance and practical advice on how to meet loading requirements and loading performance standards, the NHVR said the Load Restraint Guide 2025 is recommended reading.