Truck and trailer rules in South Australia: licence classes, trailer brakes and size limits

This page reports what the official source says. It is not legal advice: ask the office named here. The sources are five South Australian Government pages from sa.gov.au, provided by the Department for Infrastructure and Transport, and five National Heavy Vehicle Regulator (NHVR) pages, all read on October 10, 2026. The sa.gov.au pages cite the Road Traffic Act 1961 and its regulations without reproducing them here. Federal background and the other places are on the parent page, trucks and trailers for tree work.

At a glance

Item	What the sources say
Car (C)	A vehicle with a gross vehicle mass (GVM) not greater than 4.5 tonnes, towing a single trailer within the combination mass limits
Light Rigid (LR)	GVM greater than 4.5 tonnes but not greater than 8 tonnes
Medium Rigid (MR)	Two axles and a GVM greater than 8 tonnes
Heavy Rigid (HR)	Three or more axles and a GVM greater than 8 tonnes, not articulated
Heavy Combination, Multi Combination	HC: a prime mover with one semitrailer, or a rigid vehicle with a trailer over 9 tonnes GVM. MC: any vehicle or combination except motorbikes
Trailer brakes	Required when gross trailer mass (GTM) is over 750 kg; a breakaway system over 2 tonnes
Light vehicle load width	150 mm past either side of the trailer; 2.5 metres overall
Light vehicle and trailer length	19.0 metres

Licence classes

The South Australian licence classes page lists nine classes. It defines the Car class by a GVM not greater than 4.5 tonnes and lists utilities, light delivery vans and small trucks among examples. It adds that a forklift needs a high risk work licence from SafeWork SA as well. Light Rigid covers a GVM greater than 4.5 tonnes up to 8 tonnes and may tow any trailer within the towing vehicle's gross combination mass. Medium Rigid covers a two-axle vehicle over 8 tonnes and may tow a single trailer other than a semitrailer with a GVM not greater than 9 tonnes. Heavy Rigid covers three or more axles over 8 tonnes with the same 9 tonne trailer limit. Heavy Combination covers a prime mover with one semitrailer, or a rigid vehicle with a single trailer with a GVM greater than 9 tonnes. Multi Combination covers B-doubles, road trains and any other vehicle or combination except motorbikes. The page says the licence card or digital licence must be carried when driving a vehicle over 4.5 tonnes GVM.

The page on getting a heavy vehicle licence sets the experience and age lines. LR and MR need a class C licence for at least one year. HR needs class C for at least 2 years, or LR or MR for at least one year. HC needs MR or HR for at least one year, and MC needs HR or HC for at least one year. Minimum ages are 18 for LR and MR and 19 for HR and HC. Upgrades go through a vehicle-on-road test or a competency-based training course with an authorised instructor, and HC and MC use the course only. The page prints a replacement licence fee of AU$22, read October 10, 2026.

Trailer brakes, chains and towing

The Vehicle Standards page on light vehicle towing, reference MR25, applies to towing vehicles with a GVM of 4.5 tonnes or less. It says trailers must be fitted with brakes if the GTM exceeds 750 kg. Override brakes are accepted up to 2 tonnes GTM for trailers built to Vehicle Standards Bulletin 1 or the Australian Design Rules, and centre-axle trailers built to UN ECE 13 O2 are accepted up to 3.5 tonnes with a breakaway system. Where the GTM exceeds 2 tonnes the braking system needs a breakaway system that applies the brakes if the trailer disconnects. Where the maker gives no towing mass, a braked trailer with brakes operated directly by the driver may be loaded to 1.5 times the unloaded mass of the towing vehicle. A trailer with override brakes may go to the unloaded mass of the towing vehicle, and an unbraked trailer to that mass or 750 kg GTM, whichever is less. The loaded trailer mass may not exceed the tow bar and coupling rating or the maker's towing mass.

The same page asks for a secure coupling plus a safety connection such as a chain or cable. It says "A light motor vehicle may tow no more than one vehicle." Nobody may be in or on the trailer. The light trailers page says light trailers have an aggregate trailer mass under 4.5 tonnes and are built to Vehicle Standards Bulletin 1. It says from September 1, 2023 a trailer needs an entry on the Register of Approved Vehicles to be registered under the Road Vehicle Standards Act 2018.

Load and size limits

Limit	Figure as printed	Source
Load beyond a trailer side	Not more than 150 mm; total width not over 2.5 metres	sa.gov.au
Towing vehicle and trailer length	19.0 metres	sa.gov.au
Rear projection	3.7 metres at most from the axle centre; flag at least 300 mm square past 1.2 metres behind	sa.gov.au
Front projection of a load on a light vehicle	1.2 metres at most	sa.gov.au
Heavy vehicle height	4.3 metres, with listed exceptions	NHVR
Heavy vehicle width	2.5 metres; 2.55 metres for new rigid trucks and prime movers with listed safety features	NHVR
Heavy vehicle length	12.5 metres for another vehicle; combinations 19 or 20 metres	NHVR

The light vehicle loads page, reference MR143, adds that the maximum rear overhang is 60 percent of the wheelbase up to 3.7 metres, whichever is less, and that a load on a vehicle 2 metres wide may be at most 2.3 metres wide. The owner or driver is responsible for restraint under the Load Restraint Guide for Light Vehicles. The NHVR says its length rule gives 19 metres for a combination whose heavy trailer has neither ADR 38/05 brakes nor power from the towing vehicle, and 20 metres otherwise, in pages carrying amendments that commenced on August 1, 2026. The sa.gov.au light vehicle page, read on the same date, prints 19.0 metres for a light towing vehicle and trailer, so each figure is given as its page prints it. The NHVR's About us page says its National Services Transition program has transitioned heavy vehicle regulatory services in South Australia. For the heavy mass limits, the NHVR general mass limits page gives 43.5 t for a single vehicle or combination that is not named in its table and is neither a B-double nor a road train.