Commonwealth Numbered Regulations - Explanatory Statements

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Issued by the authority of the Minister for Land Transport

Interstate Road Transport Act 1985

Interstate Road Transport Regulations (Amendment)

Subsection 56(1) of the Interstate Road Transport Act 1985 (the Act) provides that the Governor-General may make regulations for the purposes of the Act. The Interstate Road Transport Regulations (the regulations) are made under that subsection. The Act and the regulations together set up the Federal Interstate Registration Scheme for interstate passenger and goods vehicles, and regulate the operation of vehicles registered under the Scheme.

The Act was amended in 1991 by the Interstate Road Transport Amendment Act 1991 (the Amendment Act) to provide for the registration and regulation of prime movers which are to be used as part of a B-double under the Federal Interstate Registration Scheme. A B-double is a vehicle combination consisting of a prime mover towing two trailers, with the prime mover being connected to the first trailer, and the first trailer to the second, by turntables.

The amendments to the regulations further provide for the regulation of Federal and State-registered trailers when operating as part of a Federal B-double combination.

The Amendment Act received Royal Assent on 2 September 1991 and is, under subsection 2(1), to commence on a day to be fixed by Proclamation. His Excellency the Governor-General in Council has fixed 15 November 1991 as the day on which the Amendment Act commences.

The regulations make provision for regulating the operation of B-doubles on Federal routes, roadworthiness, and technical requirements of B-doubles in the carriage of passengers or goods on Federal routes.

Details of the amending regulations are set out in the Attachment.

The Regulations commenced on 15 November 1991.





Makes provision for the commencement of the amendments to the Principal Regulations.


Cites the Interstate Road Transport Regulations as the Principal Regulations.


Amends subregulation 2(1) of the Principal Regulations by replacing the previous definitions of "prime mover", "semitrailer", "single axle", "tandem axle group" and "triaxle group" with new definitions consistent with those in the Australian Design Rules. The previous definition of "load sharing suspension system" has been amended to be a definition of "load sharing". The regulation also amends subregulation 2(1) of the Principal Regulations to include definitions of terms related to the technical requirements of B-doubles.


Regulation 5A of the Principal Regulations already requires most classes of heavy vehicles to be fitted with speed limiters restricting their top speed to 100 km/h. Amending regulation 4 requires B-double prime movers registered under the Act to be road speed limited to 100 km/h.


Subregulation 12A(1) of the Principal Regulations limits the maximum permitted gross mass of a vehicle registered under the Act. The maximum permitted gross mass of a B-double is set separately from that for other classes of vehicles, as authorised by section 12B(2)(a) of the Act. Regulation 5 therefore amends subregulation 12A(1) of the Principal Regulations to exclude B-doubles from its operation, and makes separate provision by way of new subregulation (3) to limit the maximum permitted gross mass of a B-double.


Amends subregulation 12B(1) of the Principal Regulations to ensure that the provisions regarding the maximum permitted gross mass on an axle group apply to B-doubles.


Adds new subregulation 12H(4) which excludes B-doubles or the components of B-doubles from the existing provisions relating to an overloaded vehicle. Separate provisions in relation to overloading of B-doubles are included in the Act.


Amends subregulation 12I(1) of the Principal Regulations to exclude B-doubles or their components from the present requirements to be weighed to determine overloading. Separate provision in this respect is made by new subregulation 12I(1A).

New subregulation 12I(1A) provides that the driver of a B-double may be directed to a weighing station to be weighed to determine overloading, and if necessary, to be unloaded to comply with mass limit provisions of the Act and regulations.

Also amends subregulation 12I(2) of the Principal Regulations to require B-doubles to obey directions at weighing stations.

Also amends subregulation 12I(3) of the Principal Regulations to exclude B-doubles from present requirements that the driver of a motor vehicle must not refuse to comply with directions at a weighing station, and inserts new subregulations (3A) and (3B) requiring the drivers of respectively, B-doubles and other vehicles to comply with such directions. This is to be done because separate penalties are to be provided for the offence of failing to comply with such directions when committed by the driver of a B-double. In the case of a B-double the penalty is set by the Act itself at $4,000.

Amends subregulation 12I(4) of the Principal Regulations to exclude B-doubles, but includes new subregulation 12I(1A) applying only to B-doubles, so that B-doubles, in common with other vehicles, are not to be required to be driven more than 5 km to comply with a direction under subregulations 12I(1), (1A) or (2). The reason for separate provision being made in the case of B-doubles is that many of the requirements for B-doubles, but not for other vehicles, are set by the Act directly. Provision has also been made for the offence of failing to comply with such a direction.


Amends subregulation 12K(1) of the Principal Regulations so that the driver of an overloaded B-double may be directed to unload enough of the load to comply with mass limits.

Amends subregulation 12K(2) of the Principal Regulations so that the penalty of $2,000 for failing to unload an overloaded vehicle does not apply to a B-double. Penalties for offences involving B-doubles are set in the Act.


Provides for a new Division 2B of Part II applying to B-doubles. The references in the new Division to the Australian Design Rules "as amended and in force from time to time" are authorised by subsection 56(3) of the Act.

New regulation 12L provides that a B-double must operate on a federal route unless:

       the driver or operator holds a current permit issued by the relevant State or Territory authority, if required; or

       a State or Territory permit is not required and the B-double complies with the regulations; or

       the driver is required by the regulations to operate in that place.

Section 43A of the Act authorises the Minister to determine federal routes for the operation of B-doubles.

New regulation 12M requires the components of a B-double combination to comply with applicable Australian Design Rules or national standards made under the Motor Vehicle Standards Act 1989.

New regulation 12N requires the prime mover and each trailer that constitutes a B-double to be marked with a Vehicle Identification Number (VIN) or a chassis number.

New regulation 120 limits the height of a B-double to 4.3 metres unless a height of 4.6 metres is approved by the State or Territory administering authority.

New regulation 12P limits the length of a B-double to 23 metres.

New regulation 12Q specifies the minimum axle spacing between axle groups and prohibits adjacent pairs of triaxle groups.

New regulation 12R provides the minimum requirements for starting on an incline and running up an incline for a B-double.

New regulation 12S provides the minimum standards for B-double brake systems. These minimum requirements apply even if the Australian Design Rules or national standards set a lower requirement for brake performance.

New regulation 12T provides minimum requirements for protection against brake failure. It also specifies standards for couplings for supply and control line hoses.

New regulation 12U requires that if the parking brake in the prime mover is applied, the parking brakes of each of the trailers must be simultaneously applied automatically.

New regulations 12V, 12W, and 12X provide minimum requirements in relation to fifth wheel assemblies and fifth wheel kingpins.

New regulation 12Y provides that B-doubles are to be fitted with spray suppression devices unless a State or Territory administering authority exempts them from this requirement for operations on unsealed roads.

New regulation 12Z provides that a B-double must track within 100 millimetres of its nominal path while travelling in a straight line on a level road. The purpose of this requirement is to minimise deviations of the path of the wheels from a straight line.

New regulation 12ZA provides minimum requirements for the distribution of a load on each axle group not equipped with variable proportioning brake systems.


Amends subparagraph 21(2)(b)(i) of the Principal Regulations so that B-double prime movers have the letter "x" as the second character in the registration plate. It also amends subparagraph 21(2)(b)(ii) of the Principal Regulations so that vehicles not registered to operate under subparagraph 21(2)(b)(i) have the letter "v" as the second character.


Replaces the previous Schedule 1B, which sets out the limits of possible axle loads for different types of axles or axle groups, with a new Schedule including provisions necessary for B-doubles.

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