This guide provides advice to heavy motor vehicle owners, operators and modifiers about the fitting and use of truck-mounted crash attenuators (attenuators).

The use of attenuators in the road construction and maintenance, traffic control and incident response sectors has steadily increased and is now a regular part of ensuring the safety of those working on and near roads.

Fitting an attenuator can result in the heavy motor vehicle exceeding dimension limits for rear overhang and overall length when deployed. National Heavy Vehicle Standards (Truck-Mounted Attenuator) Exemption Notice 2022 (No.1) (the Notice) provides the necessary exemptions from the heavy vehicle standards.

On this page

• Fitting an attenuator
  • Fitting a body
  • Chassis modifications
  • Harness seatbelt installation
• Vehicle dimensions
• Warning light
• Warning pattern
• Using an attenuator
• Resources

Fitting an attenuator

Fitting an attenuator to a heavy motor vehicle is considered a modification under the Heavy Vehicle National Law (HVNL) and requires approval by an Approved Vehicle Examiner (AVE). As fitting an attenuator results in the vehicle exceeding dimension limits when deployed, an exemption is required before the modification can be assessed and approved. Depending on what is required to fit the attenuator, there may be a number of modifications that require approval, which include:

Fitting a body

Generally, the fitting of an attenuator is approved under Vehicle Standards Bulletin 6: National Code of Practice for Heavy Vehicle Modifications (VSB6) Modification Code J1 Body Fitment.

When designing the installation, it is important to consider the position of the attenuator on the vehicle and ensure when the attenuator is deployed:

• in any position, the minimum front axle load is suitable to allow effective steering, braking and stability of the vehicle.

Note: The Performance Based Standards (PBS) steer tyre friction demand standard may be used as a reference guide regarding steer axle loading.

• The mounting location of the attenuator on the vehicle does not result in the vehicle becoming unstable or unsafe.
• The mounting location and equipment of the truck-mounted attenuator does not affect the operation or compliance of an Advanced Safety System fitted. 

• Lighting, reflectors, conspicuity markings, and rear marking plates required by the Heavy Vehicle (Vehicle Standards) National Regulation must be fitted to the rear of the attenuator/vehicle, so the vehicle complies both when the attenuator is stowed (raised) and deployed (lowered).

Note: From October 2023, the Safer Freight Vehicle amendment package permits specific vehicles to be built with an overall width of up to 2.55m. Eligible vehicles (including bodies) must not exceed maximum dimensions listed on the Register of Approved Vehicles (RAV).

More information on safer freight vehicles and the new and amended Australian Design Rules can be found in the federal Guide to Safer Freight Vehicles. 

Chassis modifications

If the installation of the attenuator requires any modifications to the vehicle’s chassis, including drilling of holes or installation of additional cross members, these modifications must be carried out in accordance with VSB6 Modification Code H4 Chassis Frame Alteration.

Harness seatbelt installation

In some cases, the attenuator manufacturer will install a harness type seatbelt designed for use while the attenuator is deployed. The NHVR would consider this a minor modification, and would not require certification provided all the following conditions were met:

• a complying seatbelt is also installed at the seating position
• the seatbelt harness or any associated mounting frame does not interfere with the normal operation of the seat or complying seatbelt
• the seatbelt harness anchorages or any associated mounting frame do not reduce the structural integrity of the seat or complying seatbelt’s anchorages
• structural modifications to the cabin are not required to fit the seatbelt harness anchorages or any associated mounting frame, and
• a label is affixed in a readily visible position advising that the harness type seatbelt is only to be used when the attenuator is deployed.

If any anchorage, seat or seatbelt requires modification, they must be certified by an AVE using the appropriate VSB6 modification code.

Note: Harness type seatbelts described above are only to be used while the attenuator is deployed are not considered to be complying seatbelts. The NHVR does not provide any specifications (forces, anchorage requirements, etc) for these harness seatbelts.

Vehicle dimensions

When designing or installing an attenuator, it is important to ensure that the completed vehicle complies with the dimension requirements of the Notice. The dimension exemptions in the Notice only apply when the attenuator is deployed. This means that when the attenuator is stowed, the vehicle must continue to comply will all regulation dimension requirements. When deployed, a vehicle may have a rear overhang of up to 7.6 m and may be up to 15m in overall length.

Warning light

A vehicle fitted with an attenuator must be fitted with a warning light to ensure other road users are made aware of the vehicle’s presence.

The Notice requires that when the attenuator is deployed, the warning light must:

• be clearly visible for at least 500m in all directions; or if it is not possible to achieve this with one warning light, additional warning lights must be used until the 500m visibility requirement is met; and
• not be a strobe light; and
• emit a yellow coloured light of rotating and flashing effect; and
• flash between 120 and 240 times a minute; and
• must not be of an intensity that is likely to dazzle another road user.

Warning pattern

To ensure the attenuator is easily seen, the Notice requires that it be fitted with a warning pattern on both sides and the rear (in the deployed configuration). 

To provide clarification, warning patterns must cover an area of at least 0.16m2 and have diagonal stripes that are at least 100mm wide, alternately coloured either:

• red and white
• black and white
• red and yellow; or
• black and yellow.

If reflective material is used in the warning pattern, the colour of reflectors used must comply with the Heavy Vehicle (Vehicle Standards) National Regulation:

• only yellow reflectors may be fitted to the side of a vehicle.
• Only white reflectors may be fitted to the front of a heavy vehicle.
• Only red reflectors may be fitted to the rear of a heavy vehicle.

For example: If the red and yellow warning pattern was fitted to the rear of a vehicle only the red striping would be permitted to be a reflective material.

Note: Where additional retro reflective materials are permitted, they must not impair the effectiveness of the mandatory lighting and light-signalling devices.

Using an attenuator

Under the Notice, the attenuator may only be deployed when the vehicle is actively engaged in an approved task.

Note: The Notice defines an approved task as when the attenuator is engaged in a road construction, repair or maintenance, traffic control operations or road incident response task.

At all other times when the vehicle is on a road, the attenuator must be in the stowed position and comply with all dimension requirements.

When the attenuator is deployed, the flashing warning light/s must be switched on.

Note: Typically, when an attenuator is deployed, the lane of the road the attenuator is deployed on is considered closed and an access authority is not required. However, if unsure the operator of the vehicle should enquire with the road manager to determine if an access authority needs to be obtained prior to deploying the attenuator.

Resources

Chain of Responsibility

The Primary Duty requires Chain of Responsibility parties to ensure, so far as is reasonably practicable, that they carry out their transport activities in a way that ensures public safety when heavy vehicles are used on a road.

Keeping up to date with vehicle standards and implementing them in your fleet is one part of your transport activities.

Complying with the national heavy vehicle safety standards

The operator of a heavy vehicle must ensure that their vehicle complies with the relevant Australian Design Rules (ADRs) and the Heavy Vehicle (Vehicle Standards) National Regulation. Using or permitting another person to use a defective heavy vehicle on a road is an offence.

A defective heavy vehicle is a vehicle that:

• does not comply with the heavy vehicle safety standards; or
• has a part that does not perform its intended function; or
• has deteriorated to an extent that it cannot be reasonably relied on to perform its intended function.

More information can be found at Heavy vehicle defects.

NHVR support

If you have questions or require further information, please contact the Vehicle Standards team.

Changes and updates