What Is a Truck Mounted Attenuator (TMA) and When Is One Required?

A truck mounted attenuator (TMA) is a heavy vehicle fitted with an energy-absorbing crash cushion at the rear, positioned behind a work area or slow-moving works to protect workers and work vehicles from errant vehicles. Whether one is required depends on road speed, traffic volume, the type of works and the traffic guidance scheme, along with state and contract requirements.

Below we explain how TMAs work, the situations where they are typically used, what NSW's new standard means, operator and inspection requirements, and how to brief and run a TMA safely on site.

How does a truck mounted attenuator work?

The attenuator is a crash cushion mounted on a frame at the back of a truck. When a vehicle runs into it, the cushion collapses in a controlled way, absorbing much of the impact energy. That does two things:

• Protects the workers and plant ahead by stopping the errant vehicle before it reaches them.
• Reduces injury to the occupants of the striking vehicle compared with hitting a rigid truck or barrier.

Most attenuators fold up for travel and fold down for deployment. Many TMAs also carry an arrow board or other warning devices, making the truck itself a highly visible warning to approaching traffic.

The truck's weight matters too. A TMA is designed to roll forward a controlled distance on impact, so the gap between it and the work area (the roll-ahead distance) has to be right. Too close, and the truck can be pushed into the workers it is meant to protect.

When is a TMA required?

There is no single answer that applies to every job in Australia. The need for a TMA is usually decided by a combination of:

• Speed of traffic. Higher speeds mean greater impact energy and greater consequences if a vehicle enters the work area.
• Traffic volume. More vehicles means more chances of an intrusion.
• Type of works. Static works, mobile works (such as line marking, sweeping or pothole patching) and short-term works all carry different exposures.
• Worker exposure. How close workers are to live traffic, and whether there is a safe buffer or barrier.
• The traffic guidance scheme. The TGS for the job, prepared by a suitably qualified person, shows where a TMA is needed and how it is positioned.
• State standards and contract conditions. Road authorities and principal contractors can require TMAs beyond the minimum.

TMAs and the hierarchy of controls

A TMA is a separation control. Under the hierarchy of controls, the first questions are whether the hazard can be eliminated (closing the road or diverting traffic) or traffic separated from workers by barriers. Where workers must work close to live traffic and permanent barriers are not practical, a TMA provides a protective buffer. Speed reduction, warning devices and PPE then add further layers. A TMA does not replace these; it works with them.

The NSW change

In NSW, Transport for NSW replaced the Traffic Control at Work Sites Technical Manual (TCAWS) Issue 6.1 with TS 05492:1.0 Traffic Control at Work Sites on 25 June 2026. The new standard adds requirements on crash attenuators, as well as end-of-queue management and temporary speed zoning. Some supporting checklists and templates were still being developed at the time of release, and some councils or contracts may still reference the older manual. Our guide to what changed from TCAWS to TS 05492 covers this in more detail.

Other states

Queensland, Victoria and the other states apply the national Austroads Guide to Temporary Traffic Management with their own supplements, and their requirements for crash attenuators may differ from NSW. Always check the state documents and the contract.

Common situations where TMAs are used

These are typical uses, not a rule. The TGS and the applicable standard decide what a specific job needs.

Who can operate a TMA?

TMA operators need:

• The correct heavy vehicle licence for the truck being driven.
• Appropriate traffic control training for their state. In NSW, SafeWork NSW issues Traffic Control Work Training cards; other states have their own arrangements.
• Induction on the specific unit, including deployment, travel mode, controls and emergency procedures.
• Fitness for work, including managed fatigue. TMA shifts often run at night or on long motorway jobs. See our guide to fatigue management for traffic controllers.

A TMA operator sits in the vehicle most likely to be hit on site. They should wear a seatbelt, keep the head restraint correctly adjusted, keep the cabin free of loose objects and never leave the vehicle in the impact zone on foot.

TMA inspection and certification

Units must be inspected and certified in line with the manufacturer's requirements and the relevant guideline, and after any impact, however minor it looks. A damaged cushion may not perform as designed next time.

Daily pre-start checklist for a TMA

For a broader daily routine for the whole crew, see our traffic control pre-start checklist.

Running a TMA on site

A well-run TMA operation follows a routine:

1. Briefing. The team leader briefs the crew on the TGS, the TMA's position, the roll-ahead gap, escape routes and radio channels. The SWMS should cover TMA tasks specifically; see our SWMS for traffic control guide.
2. Positioning. The TMA is placed in the location shown on the TGS, with the correct gap to the work area and wheels set as the operator procedures require.
3. Deployment. The cushion is lowered, warning devices switched on and the operator confirms readiness by radio.
4. Mobile works. For moving works, the TMA follows at the planned distance, adjusting to keep protection in place through curves and over crests.
5. Monitoring. The operator watches mirrors for approaching vehicles and alerts the crew by radio to anything unusual.
6. Pack-down. The TMA stays in place to protect the crew while devices are removed, then is stowed for travel.

Common TMA mistakes

• Wrong roll-ahead gap. Too close puts workers at risk; too far invites vehicles to cut in.
• Workers standing between the TMA and the work area in the roll-ahead zone.
• Using an uncertified or damaged unit after a minor bump that nobody reported.
• TMA arriving late, so the crew sets up without protection.
• Operators on excessive hours. Fatigue is a major hazard on long night shifts.

Questions to ask before you book a TMA

If you are a client or principal contractor, these questions help you compare providers and avoid surprises on the day:

1. Does the TGS call for a TMA, and in which positions? Get the requirement confirmed in writing by the person who prepared the plan.
2. Is the attenuator certified, and when was it last inspected? Ask to see current certification.
3. What licence and training does the operator hold? Confirm the heavy vehicle licence class and traffic control training for your state.
4. Will the TMA be on site for set-up and pack-down? Those are often the most exposed periods for the crew.
5. How is the TMA priced? Ask whether it is a separate line item, what the minimum shift is, and whether travel is charged.
6. What happens if the TMA breaks down or is hit? Find out whether a backup unit is available, and whether works must stop until protection is restored.
7. How are operator hours managed? Long motorway and night shifts need clear fatigue limits.

TMAs are usually quoted separately from traffic controllers, and minimum charges for vehicles and operators of six to eight hours are common. Prices vary widely by provider, location, time of day and job, so get itemised written quotes.

What if a TMA is hit?

Help anyone injured and make the site safe. A notifiable incident must be reported to the WHS regulator and the site preserved, except to help people or make it safe. Remove the unit from service until it has been inspected and certified, and record the event. Our guide to traffic controller safety covers incident response in more depth.

Next steps

If you are booking traffic control on a higher-speed road, ask your provider whether the TGS calls for a TMA and how it is priced. If you run a traffic control company, TrafWise helps you roster licensed TMA operators within fatigue limits and record checks on digital dockets.