Key takeaways
- Cones warn and guide drivers, tested safety barriers installed as a system can contain or redirect a vehicle, and a closure removes the traffic.
- Work through the hierarchy of controls: eliminate traffic first, then separate, then reduce speed, then warn.
- Speed, traffic volume, how close people work to traffic, how long the hazard stays and the space available decide the choice.
- A safety barrier needs room behind it to deflect and suitable end treatments; without that space it may give a false sense of protection.
- The approved TGS, prepared by a suitably qualified person, makes the final choice; crews must install exactly what it shows.
Choosing cones vs barriers vs a full closure comes down to how much protection the work needs: cones warn and guide, tested safety barriers can contain or redirect a vehicle, and a closure removes traffic altogether. Speed, traffic volume, how close people work to traffic, how long the hazard stays and the space available decide which one fits.
This article explains how that decision is made and walks through five example sites. The examples are teaching scenarios, not real projects, and the final decision belongs in the approved traffic guidance scheme (TGS), which must be prepared by a suitably qualified person. This is general information, not legal or engineering advice.
Start with the hierarchy of controls
Work health and safety law expects risks to be controlled using the most effective measures that are reasonably practicable. For roadworks, that hierarchy usually looks like this:
- Eliminate: close the road and detour traffic, or do the work when the road is closed for another reason.
- Separate: keep vehicles physically away from people, with safety barriers or a truck-mounted attenuator.
- Reduce speed: lower the approach speed through an approved temporary speed limit.
- Warn and guide: signs, cones, bollards, delineation, arrow boards and VMS.
- Personal protective equipment: hi-vis and other PPE as the last line.
Cones sit at step 4. They are essential, but they are not protection. A cone tells a driver where the lane is; it does not stop a car whose driver is not looking. That is the core of every cones-versus-barriers decision. For WHS duties on road work, see Safe Work Australia and our guide to WHS duties for road work.
What each option actually does
| Option | What it does | What it does not do | Typical needs |
|---|---|---|---|
| Cones, bollards, barrier boards | Guide traffic, mark the work area edge | Stop or redirect a vehicle | Correct spacing and size per the TGS, maintenance during the shift |
| Pedestrian barriers and fencing | Separate pedestrians from hazards | Protect against vehicles | Continuous route, kerb ramps, stability |
| Water-filled barriers | Some are tested to redirect vehicles at certain speeds; others delineate only | Protect beyond their tested conditions | Test information, length, connections, space behind |
| Concrete or steel safety barriers | Contain or redirect errant vehicles when installed as a tested system | Work without deflection space and end treatments | Working width behind, terminals, installation per manufacturer |
| TMA | Absorbs the impact of a vehicle running into the back of the work area | Protect from side impacts | Correct position, trained and licensed operator, inspected unit |
| Full closure | Removes traffic from the work area | Remove traffic risks on the detour | Approval, detour, notifications |
Two details catch people out with barriers. First, a safety barrier deflects when hit, so it needs space behind it that is kept free of workers, plant and materials. Our guide to safety barrier deflection and working width explains this. Second, water-filled barriers vary widely; see water-filled vs concrete barriers before assuming a row of them protects anyone.
The decision factors
The TGS designer weighs the factors below together. None of them decides the answer on its own, and the thresholds come from AS 1742.3, the Austroads Guide to Temporary Traffic Management (AGTTM), the state's requirements and the barrier manufacturer, not from a rule of thumb.
| Factor | Pushes towards cones | Pushes towards barriers | Pushes towards closure |
|---|---|---|---|
| Speed | Low | Higher | Very high with no room |
| Traffic volume | Low | Moderate to high | High with no alternative arrangement, or low with a good detour |
| Distance between workers and traffic | Generous | Small | None |
| Duration | Short, attended | Days or weeks, or left overnight | Short and intense, or work occupies the whole road |
| Hazard left behind | None | Excavations, drop-offs, stockpiles | Hazard across the whole road |
| Space available | Enough for delineation | Enough for barrier, working width and terminals | Not enough for either |
| Detour available | Not needed | Not needed | A workable route exists |
Five example sites
Example scenario A: line-marking touch-up in a 50 km/h shopping centre access road. Short, attended, low speed and low volume, with workers moving along the line. In this example the TGS uses cones and signs with a work vehicle, and a lookout. Barriers would take longer to place than the work itself, and the crew's exposure while installing them would outweigh the benefit.
Example scenario B: a deep excavation next to a 70 km/h arterial, open for two weeks. Workers are in and around the hole every day, and the hole is left open overnight. Cones would leave a drop-off next to traffic for two weeks, protected by nothing. In this example the TGS specifies a tested safety barrier system along the excavation with its working width kept clear, terminals at each end and a lane closure to make room. This one is walked through in detail below.
Example scenario C: replacing a bridge expansion joint on a narrow two-lane road. The joint runs across the full width. There is no room for traffic and a barrier on the bridge. In this example the TGS uses a full closure overnight with a signed detour, which is quicker and safer than staging the work half-width under stop/slow over many shifts. See road closure and detour plans for how closures are planned.
Example scenario D: footpath reconstruction beside a 60 km/h road. The hazard for pedestrians is the open footpath; the hazard for workers is the traffic lane next to them. In this example the TGS uses pedestrian barriers to separate people from the excavation, a signed pedestrian detour, and cones and a parking lane closure to keep traffic away from the work edge. Whether a safety barrier is needed depends on how close the work is to the live lane and for how long, which the designer assesses.
Example scenario E: kerb and gutter works on an 80 km/h road for a week. Workers are close to the lane edge for long periods. In this example the designer compares two options: a lane closure with a temporary speed reduction and cones, or a safety barrier along the kerb line. The barrier needs a working width that would push it into the remaining lane, so the designer chooses the lane closure with reduced speed and a TMA. This is the kind of trade-off that should be written into the TGS notes.
Worked example: site B, step by step
Here is how scenario B plays out on a typical job.
- Design. The designer confirms the barrier type, length, terminals and the working width from the manufacturer's information, and checks there is room for traffic, the barrier and its working width. A lane closure is needed to make that room.
- Approval. The road authority approves the TGS and the lane occupancy.
- Installation. Barrier installation is itself a high-risk activity, done under a separate set-up: a lane closure with a TMA behind the installation crew, in the order the installer's procedure specifies. Each unit is connected as the system requires.
- Check. The supervisor and the installer check the barrier against the TGS and the manufacturer's requirements, including the end treatments, and record it with photos.
- Working width marked. The space behind the barrier is marked and briefed: no workers, plant or materials in it.
- Daily inspection. At the start and end of every shift and at intervals during it, the crew checks for damage, displaced units, loss of water or ballast where relevant, and anything stored in the working width.
- After an impact. The area is made safe, the incident reported, and the barrier inspected and repaired or replaced before work resumes behind it.
- Removal. The barrier comes out under a set-up again, in reverse order.
What goes wrong in this example, and the fix: a delivery is stacked against the back of the barrier on day four, inside the working width. The mid-shift inspection finds it. The supervisor has it moved and adds "nothing in the working width" to the daily toolbox talk. If the stack had been there when a truck hit the barrier, the barrier would have pushed the materials into the work area.
Common mistakes when choosing and using separation
- Treating a line of cones as protection. Cones mark the edge. If workers are relying on them to stop a vehicle, the plan needs a different control.
- Using any barrier as a safety barrier. Pedestrian barriers, fencing and untested water-filled units do not protect workers from traffic. Know which product you have and what it is tested for.
- Barrier with no room behind it. A safety barrier installed hard against an excavation or a stockpile has nowhere to deflect. The working width is part of the system.
- Leaving out the ends. An untreated barrier end can itself become a hazard for drivers. End treatments are specified for a reason.
- Swapping methods on site. Replacing barriers with cones because the truck did not turn up, or extending a closure because it is easier, changes the risk the TGS was designed for. Stop and get the change assessed.
- Ruling out a closure too quickly. Closures feel disruptive, but a short, well-advertised closure can expose the crew and the public to far less risk than weeks of staged work beside live traffic.
- Forgetting overnight. What is enough while the crew is present and watching may not be enough when the site is left unattended. Our guide to the clear zone at roadworks covers hazards left overnight.
A printable checklist for the site
| Check | Cones and delineation | Safety barrier | Full closure |
|---|---|---|---|
| Matches the TGS layout and revision | ☐ | ☐ | ☐ |
| Correct device type and size | ☐ | ☐ | ☐ |
| Spacing or connections as specified | ☐ | ☐ | n/a |
| Working width clear | n/a | ☐ | n/a |
| End treatments in place | n/a | ☐ | n/a |
| Closure points and detour signs in place | n/a | n/a | ☐ |
| Pedestrian route continuous and accessible | ☐ | ☐ | ☐ |
| Inspected at start, during and end of shift | ☐ | ☐ | ☐ |
For the standards behind these devices, see AS 1742.3 through Standards Australia and the AGTTM through Austroads.
Next steps
Before your next job, ask the designer which option the TGS uses and why, and brief the crew on what that option does and does not protect against. If you run a traffic control company, TrafWise keeps pre-starts, SWMS sign-ons and equipment records together; you can start a free trial.
Frequently asked questions
What is the difference between cones and barriers at roadworks?
Cones and other delineation devices guide drivers and mark the edge of the work area, but they offer no physical protection if a vehicle leaves its lane. Safety barriers that have been tested and installed as a system can contain or redirect an errant vehicle. Pedestrian barriers separate people from hazards but are not designed to stop vehicles.
When are concrete or steel barriers needed at roadworks?
Usually when workers or hazards such as deep excavations will be close to fast or busy traffic for an extended period, or are left overnight. The traffic guidance scheme designer decides, using AS 1742.3, the AGTTM, state requirements and the barrier manufacturer's information on deflection and installation. Short, low-speed jobs may not need them.
Do water-filled barriers stop cars?
Some water-filled barrier systems are tested to redirect vehicles at certain speeds when installed exactly as tested, with the required length, connections and space behind them. Others are only for delineation or pedestrian separation. Check the product's test information and the TGS before relying on any barrier to protect workers from traffic.
When should you close a road instead of using barriers?
When there is not enough room for traffic and a barrier with its deflection space, when the work takes up most of the road, when exposure would otherwise be high, or when a short closure is safer and quicker than a long staged job. A full closure needs road authority approval and a workable detour.
Who decides between cones, barriers and a road closure?
The traffic guidance scheme designer, working with the principal contractor and the road authority, based on a risk assessment and the relevant standards. Crews do not swap one method for another on site. If conditions differ from what the TGS assumed, the supervisor stops and gets the change assessed and approved.