A traffic controller is only safe if approaching drivers can see them in time to stop. Sight distance is the length of clear road between the first point where a driver can see the controller, device or queue and the position itself. This checker works out the distance the current rules require and compares it with what you have on site.
In NSW the rules come from Transport for NSW's TS 05492 Traffic Control at Work Sites, which replaced the old TCAWS manual on 25 June 2026. Many traffic guidance schemes still quote the old manual, so it pays to check against the new one.
How Dimension D works
Most NSW sight distances are a multiple of one number: D. D is the speed of the zone drivers are in before they reach the point you're checking, expressed in metres.
- A driver approaching through a 60 km/h zone gives D = 60 m.
- In a series of zones (100, then 80, then 60, then 40 km/h), D lags one zone behind: 100, 100, 80 and 60 m.
- D can be the lower of the permanent and the temporary limit. Where the risk that drivers won't slow down is higher, the PWZ-qualified designer can use the permanent or approach speed throughout.
- D is not used to set the length of speed zones.
Because D is so simple, a traffic controller can work out the requirement on the spot. The hard part is measuring what the site actually gives you, which is why the tool can measure it with your phone.
Sight distances the rules require
These are the D-based distances in TS 05492, shown at an 80 km/h approach (D = 80 m):
| What you're checking | Rule | At D = 80 m | Clause |
|---|---|---|---|
| Traffic controller, STOP/SLOW bat or portable traffic control device | at least 1.5 × D | 120 m | Table 73, s13.6.4 |
| End of queue, open road | 2 × D | 160 m | Table 73 |
| End of queue, urban | 1.5 × D | 120 m | Table 73 |
| Intermittent work with a lookout | 3 × D | 240 m | Table 87 |
| Intermittent work without a lookout | 6 × D | 480 m | Table 87 |
| Gap between tapers on multi-lane roads | 1.5 × D | 120 m | Tables 73 and 75 |
Shuttle flow on a two-lane road is different. Table 47 sets a minimum clear sight distance to oncoming traffic based on the work area length L: 300 m if the work area is under 60 m, otherwise L + 250 m, at speeds up to 100 km/h. That number also decides whether one traffic controller is enough (Table 46).
Which device is allowed at the speed
On TfNSW work sites, TS 05492 Table 44 limits STOP/SLOW bats to roads with a permanent speed of 50 km/h or less. Manually operated portable traffic control devices are allowed up to 60 km/h, and remotely controlled devices such as portable traffic signals and boom barriers at any speed.
Bats are still allowed above 50 km/h in listed situations, including:
- incident and emergency response
- a controller position in place for less than 60 minutes
- traffic stopped 4 or fewer times an hour
- roads under 200 vehicles a day that end at a T-junction
- controllers moving within the work zone, such as resurfacing
The checker flags when the speed is over the limit for the device you're using.
Measuring sight distance on site
Measure from the point drivers first get a clear view of the position, along the line they drive, to the position itself. Do it from a safe place off the road.
- Stand at the position you're checking: the controller's spot, the device, or the expected back of the queue.
- Tap Start here and wait for a GPS fix. The tool waits until accuracy is better than about 25 m.
- Walk towards approaching traffic, staying off the road, to the furthest point where the position is still clearly visible. Watch for crests, bends, trees, parked vehicles and plant.
- Tap Stop. The distance goes into the form and the result updates.
Phone GPS is usually good to a few metres in open sky, but less so near tall buildings or under trees. When the result is within about 10% of the limit, pace it or use a measuring wheel before you rely on it.
What to do when it fails
A fail means drivers may not see the controller or the queue in time to stop. Don't start work in that position. Common fixes:
- move the controller back from the bend or crest so they're seen sooner
- clear what blocks the view if it's safe and allowed
- add PREPARE TO STOP signs or queue warning ahead of the expected end of the queue
- add a lookout for intermittent work, which halves the requirement from 6D to 3D
- use two controllers with radios, or portable traffic signals, for shuttle flow
Moving signs or changing the layout beyond the tolerances is a TGS change. Mark any moved sign on the site copy of the TGS and talk to the designer. Our guides on stopping sight distance at work zones and end of queue management go further.
A worked example
A crew is setting up stop/slow on a rural road with an 80 km/h permanent limit. The TGS drops traffic to 60 km/h ahead of the controller, so drivers reach the controller from a 60 km/h zone and D = 60 m.
- Required sight distance to the controller: 1.5 × 60 = 90 m.
- The controller walks back from the position and measures 84 m to the crest. That's 6 m short, so it fails.
- Moving the controller 15 m further from the crest gives 102 m. It now passes.
- The permanent speed is 80 km/h, so on a TfNSW site a bat isn't allowed unless an exemption applies. The crew uses a portable traffic control device instead.
Queensland and other states
Queensland builds on the Austroads guide (AGTTM) with its own differences in QGTTM Part 3. Sign spacing there is 15 m up to 55 km/h, 45 m from 56 to 65 km/h and equal to the speed above that, doubled for a single sign. The sight distance to a traffic controller comes from AGTTM Part 7 and your TGS. The tool shows the Queensland figures we hold and says clearly when a value must come from the TGS.
Victorian, WA and SA tables aren't loaded yet because we haven't verified them, so the tool won't guess. Use the distance on your approved TGS. Planning the whole layout? The sign layout builder lays out every sign from the same rules.