Operators planning to use the revised 20-metre combination length need to distinguish between what the road rules permit and what a semitrailer is approved to be built or modified to do.
The National Heavy Vehicle Regulator’s Vehicle Standards Guide 38 (VSG38) addresses a mismatch created when amendments to the Heavy Vehicle National Law and its Mass, Dimension and Loading Regulation commenced on 1 August 2026. The changes allow qualifying combinations up to 20 metres, but relevant semitrailer dimensions under Australian Design Rule 43/04 have not been aligned.
What changed?
For semitrailers used in combinations longer than 19 metres and no longer than 20 metres, VSG38 identifies an increase in the maximum rear overhang from 3.7 metres to 4.0 metres, subject to a limit of 60 per cent of the relevant articulation-to-overhang-line distance if that is less. The point-of-articulation to rear-overhang-line limit increases from 9.5 metres to up to 10.5 metres, subject to the applicable vehicle geometry, while the articulation-to-trailer-rear limit increases from 12.3 metres to 14.5 metres.
Those figures are not a blanket approval for every trailer. The NHVR’s published length guidance also sets conditions for combinations over 19 metres, including applicable trailer braking requirements. Other dimensional and safety requirements continue to apply.
New trailers and existing equipment follow different paths
A manufacturer building a semitrailer to take advantage of the revised limits must seek a non-standard vehicle type approval or concessional entry on the Register of Approved Vehicles through the Commonwealth department. The NHVR says VSG38 can serve as its in-principle support for applications relating solely to the 20-metre provisions, but it does not replace the federal application.
For an in-service semitrailer, modifications must comply with Vehicle Standards Bulletin 6 and be approved by an Approved Vehicle Examiner. Where a change exceeds an ADR dimension, the required in-service vehicle-standards exemption must be obtained before certification. Work outside VSB6’s scope requires the NHVR’s complex-modification process.
What should an operator check?
Before ordering a longer trailer or modifying one already in service, confirm the complete combination’s eligibility, braking system, relevant dimensional measurements, approval documentation and intended operating network. The critical question is not simply whether a combination measures 20 metres, but whether its individual components and use satisfy the applicable requirements.
The guide does not announce a new length increase in October: the legislative change commenced in August, and VSG38 was first published on 11 September. It clarifies how manufacturers, modifiers and operators should manage the resulting standards gap.
Primary sources: NHVR Vehicle Standards Guide 38 and NHVR length requirements.