New notice delivers smarter, more productive road train transport

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A new notice for road train prime movers will ease pressure on the road network, improve fatigue management and increase the efficiency of Australia’s heavy vehicle fleet.

The National Road Train Prime Mover Mass and Dimension Exemption Notice 2021 came into effect on 1 June 2021, following widespread consultation between the NHVR, road managers and industry groups.

The Notice gives road train prime movers access to more networks when operating in combinations other than a road train, such as B-doubles and single semi-trailers, or on their own.

The Notice will apply in all states and territories operating under the Heavy Vehicle National Law, except Tasmania.

The Notice resolves several long-standing issues faced by road train operators, while also enhancing road safety, efficiency and productivity. It impacts decoupling, steer mass limits and combination lengths.

Decoupling: The Notice provides flexibility for operators when decoupling their road train to continue their travel. The additional length and mass limits allow larger road train prime movers to be used in smaller combinations, such as B-doubles, single semitrailers or on their own (operating ‘bob-tail’). This avoids operators having to use a different, smaller prime mover after decoupling and will reduce traffic movements.

Steer mass limits: To date, road train steer mass limits have been restricted to prime movers being used in a road train configuration. The Notice enables road train prime movers to operate at road train steer mass limits when used in all eligible combinations listed in the Notice.

Longer combinations: The Notice allows longer total combination lengths, including the 20m prime mover and semitrailers, 27m B-doubles, and 26m prime mover semitrailer and unladen converter dolly combinations. The increase in combination lengths is to accommodate the additional length of road train prime movers. The Notice does not provide any increase to trailer dimension limits.

The Notice allows 27m B-doubles on road train networks, but not B-double networks.

The new Notice will provide road train prime mover operators with greater flexibility in managing their fleets, by allowing:

  • more efficient use of vehicle types, including bonneted prime movers
  • increased use of standardised trailer sets
  • more-productive decoupling processes
  • increased use of bull bars and other front-end protection devices
  • future investment in prime movers with larger sleeping cabs to improve driver comfort and better manage fatigue.

The National Class 3 Road Train Prime Mover Dimension and Mass Exemption Notice 2021 and supporting information, including the online operator’s guide, can be accessed online at