Trailer brakes: what the rules require, by trailer mass

When does a trailer or caravan need brakes in Australia? The 750 kg and 2,000 kg thresholds, breakaway systems, brake controllers and unbraked towing limits.

Facts checked 25 Sep 2026

The short version

Australian trailer brake rules step up at two points: 750 kg and 2,000 kg. Most people assume those figures refer to the trailer's ATM. They don't. The rules use GTM, the gross trailer mass.

The national guide for trailers up to 4.5 tonnes, Vehicle Standards Bulletin 1 (VSB1), is explicit: braking requirements are specified in terms of GTM, not ATM. GTM is the rated mass the trailer carries on its own tyres when fully loaded and hitched. It leaves out the tow ball load, so it is lower than ATM. See ATM vs GTM.

The requirements below come from VSB1 and the Australian Design Rule for trailer brakes, ADR 38/05. Transport for NSW and the WA Department of Transport describe the same steps.

The thresholds

Trailer GTM	What the rules require
Up to 750 kg	No brakes required. If brakes are fitted, NSW says they must still comply.
Over 750 kg, up to 2,000 kg	An efficient service brake. It may act on one axle only (NSW says both wheels of at least one axle). Over-run brakes are allowed.
Over 2,000 kg	Brakes on all wheels. No over-run brakes. A breakaway system.

WA's guide words the lowest step slightly differently. It says trailers of 750 kg GTM or more must have brakes, unless specifically approved by the WA Department of Transport. VSB1 and NSW say brakes are not needed up to and including 750 kg.

Up to 750 kg GTM

With no brakes required, the towing vehicle does all of the stopping, so the vehicle's own unbraked towing limit matters (see below).

750 kg to 2,000 kg GTM

As the table shows, a service brake on one axle is enough here.

This is also the only band where over-run brakes are allowed. They work mechanically, and are also called mechanical override brakes. When the tow vehicle slows, the trailer pushes forward on its coupling, and that movement applies the trailer's brakes. After backing up, disengage the reversing catch, or the brakes won't work.

Any other type of trailer brake must be operated by a signal from the tow vehicle.

Over 2,000 kg GTM

The table's three changes, in more detail:

The brakes must operate on all wheels.
Over-run brakes are not allowed. The braking must be controlled from the tow vehicle.
A breakaway system is required. If the trailer comes off the tow vehicle, its brakes must apply immediately and automatically and stay on for at least 15 minutes.

RACQ and RACV describe this band as needing electric brakes, but that is their description, not the rule. The rules themselves don't name a type. They require all-wheel brakes controlled from the tow vehicle, plus breakaway. In practice, most caravans in this band use electric brakes and a brake controller.

Brake controllers

Electric trailer brakes need a brake controller fitted in the tow vehicle. It sends the signal from the tow vehicle that the rules above call for, applying the trailer's brakes when you brake.

NSW says trailer brakes must be operable from the driver's seat. RACQ describes the usual set-up as a manual control within reach of the driver.
Electric brakes can usually be applied on their own, without the vehicle's brakes, and the trailer's braking force can be adjusted.
A controller lets you set how hard the trailer brakes compared with the vehicle, and apply the trailer brakes by themselves to help control sway.

That last point is why a controller matters when things go wrong. If a trailer starts to sway, avoid the vehicle's brakes except as a last resort. If the trailer's brakes can be applied by themselves, apply them gently. Otherwise, hold a steady speed or accelerate slightly until the sway stops. Sway control devices and electronic trailer sway control are covered in weight distribution hitches.

Breakaway systems

A breakaway system is the third requirement over 2,000 kg GTM: it applies the trailer's brakes if it separates from the tow vehicle, and keeps them on for the 15 minutes above. On caravans it often runs from a battery on the trailer.

Check it before each trip. Make sure the breakaway device works, its battery is charged, and its cable is attached to the tow vehicle's chassis.

Unbraked towing limits on the vehicle

The trailer's rules are only half of it. The vehicle also has a limit on how much it may tow without trailer brakes.

WA's guide says a vehicle's maximum unbraked towing capacity can't be more than the lesser of the manufacturer's figure or 750 kg.
Many vehicles have an unbraked figure in the owner's manual. Use the figure for your exact variant.
Where the manufacturer hasn't given a figure, the states differ. NSW says the limit is the tow vehicle's own unladen mass for a trailer that doesn't need brakes. Queensland gives 750 kg as a guide for vehicles built before 1 January 1992.

There is a catch, and it comes back to GTM. As in the short version, the brake rule follows the trailer's GTM rating. The towing limit is compared with what the trailer actually weighs, loaded, including the part on the tow ball. So a trailer that legally needs no brakes can still weigh more than the vehicle may tow unbraked. Weigh it loaded (see how to weigh your rig).

Where these rules come from

VSB1 and ADR 38/05 set the rules a trailer must be built to. Each state applies its own rules to trailers on the road, and adds its own details. VSB1 also notes that its braking chapter is under review, so check the current version. If you are unsure whether your trailer's brakes comply, ask your state road authority. See state towing rules.

Common questions

Does a 750 kg trailer need brakes?

Under VSB1 and NSW's rules, a trailer with a GTM of 750 kg or less doesn't need brakes. As noted under the table, WA words it as brakes being required at 750 kg or more. Check the GTM on the trailer's plate, and your state's rules.

Is the brake threshold based on ATM or GTM?

GTM, as VSB1 states directly (see the short version above). A trailer's ATM can be over 2,000 kg while its GTM is 2,000 kg or less.

Do I need an electric brake controller?

If your trailer has electric brakes, yes. The controller in the tow vehicle is what applies them. Over 2,000 kg GTM, over-run brakes aren't allowed, so the brakes have to be controlled from the tow vehicle.

How long must breakaway brakes stay on?

At least 15 minutes after the trailer separates, under VSB1 and ADR 38/05, as above. This applies to trailers over 2,000 kg GTM.

Sources

Authorities

Motoring associations (advice)