Do operators need PBS if they have a Road Train Prime Mover?

by admin

Do operators need PBS if they have a Road Train Prime Mover?



Since the 1st of June 2021 road train registered prime movers are allowed overall lengths of up to 20 m for semi-trailers and 27 m for B-doubles in the Australian Capital Territory (ACT), New South Wales (NSW), Queensland (QLD), South Australia (SA) and Victoria (VIC). Complying road train prime movers are also allowed 7.1 tonnes on the steer axle.

Road Train Prime Mover

The details are outlined in the National Class 3 Road Train Prime Mover Mass and Dimension Exemption Notice 2021 (No.1).

On face value this appears to be the easy way to get increased access for longer combinations. However, the notice is quite restrictive and in most states 20 m semi-trailers are only allowed on the B-double network and 27 m B-doubles are only allowed on road train networks.

Notable exceptions are South Australia where a 20 m semi-trailer with road train prime mover is allowed on the PBS Level 1A network under the notice and the ACT where a 27 m B-double is allowed access the B-double network.

Therefore, PBS remains the main pathway for 20 m semi-trailers to get general access (and/or PBS Level 1 network access) and for 27 m b-doubles to get PBS Level 2 network access (equivalent to 26 m B-double access).

PBS has proven popular for operators wanting to operate longer wheelbase prime movers with existing prescriptive trailers. Whilst the payload capacity is generally not greater, it provides more productivity through greater fleet utilization and greater safety and amenity for drivers operating long distances that require larger sleeper births.

Longer prime movers coupled with quad-axle semi-trailers are another option under PBS. Many of these exceed 20 m in overall length and are limited to the PBS Level 2 (B-double) networks. However, they can have up to 32 Pallet spaces. Quad-semi trailers can work within 20 m overall length and meet PBS Level 1 requirement with the appropriate prime mover and trailers with up to 28 Pallet spaces.

Getting PBS Level 2 network access for longer prime movers towing prescriptive B-doubles is possible, although generally more difficult since it is harder to meet PBS Level 2 swept path requirements on a conventional B-double set with longer prime mover and road managers have a hard 26 m length limit for B-double and PBS Level 2A networks. Therefore, 27 m B-doubles can only expect the PBS level 2B 30 m network or specific route access.

The Level 2B network is expanding in all states; and the Victorian 30 m PBS Level 2B cubic network almost aligns with the 26 m B-double network. However, there are notable exceptions, particularly local roads which lag state road managers in adding roads to PBS networks.

The NHVR National Class 3 Road Train Prime Mover Dimension and Mass Exemption Notice 2021 provides other access benefits, including 7.1 tonnes general access on complying road train prime movers across in most jurisdictions and road train prime movers towing converter dollies. The rational for the notice was to provide operators greater flexibility in managing their fleets by:

  • Avoiding operators’ need to use a separate, smaller prime mover to haul trailers after decoupling a road train combination – i.e., one prime mover can be used for the entire trip instead of two.
  • Allowing the use of bonneted prime movers.
  • Increasing the use of standardised trailer sets instead of shorter trailers to accommodate the length of the prime mover.
  • Facilitating a more productive decoupling process.
  • Future-proofing investment in prime movers with larger sleeping cabs to improve driver comfort and better manage fatigue.

However, this is all very much in the context of the road train network. It is not designed for getting high productivity vehicles for PBS Level 1 (General Access) and PBS Level 2 (B-double) networks. PBS remains the best option for operators seeking broader access and higher productivity vehicles.


Registration charge codes for multi-combination prime movers. Note: A Road Train Prime Mover is defined as a prime mover fitted with a tandem-drive axle group registered as a multi-combination prime mover capable of towing two or more trailers. To identify an eligible prime mover, the registration configuration charging codes can be found on the papers or via the NHVR Registration Checker app.


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