An end of queue calculator answers the question every stop/slow and portable signal job raises: how far back will the traffic stack up, and where do the warning signs go so drivers stop in time? Rear-end crashes into stopped queues are one of the most serious risks at a traffic control site, and the signs only work if they are placed back from where the queue actually ends, not from the controller.
This planner estimates the queue with your state's published method, then places the PREPARE TO STOP and ROADWORK AHEAD signs from the predicted end of that queue. In NSW it also gives the end-of-queue risk level and the treatments TS 05492 asks you to choose from.
How to calculate queue length
Each state uses a slightly different method. All three start from how many vehicles arrive while traffic is held, then multiply by an average length per vehicle that includes the gap between them.
| NSW (TS 05492) | Queensland (QGTTM Part 3) | WA (Main Roads fact sheet) | |
|---|---|---|---|
| Count | at least 15 minutes at the busiest time | 5 minutes at peak, for that approach only | hourly volume in the direction of travel |
| Stopping time | stop to release in the next cycle | maximum stopping time, including travel through the closure | work stop plus a clearance time from a table |
| Light vehicle | 8.5 m | 6 m | 8.5 m |
| Heavy vehicle | 22 m (B-double 29 m) | 20 m | 22.5 m metro, 39.5 m regional |
| Safety factor | plus 30%, round up to 10 m | at least one car plus one heavy vehicle | none stated |
Part vehicles are always rounded up. In Queensland, Table 4.3 turns the 5-minute count into multipliers for other stopping times, but the table is an image in the PDF. The planner scales the 5-minute count by the stopping time and flags the result so you can check it against the table.
If you are counting on site, the queue counter tallies cars, trucks and B-doubles as they arrive and feeds the same method.
Where the PREPARE TO STOP signs go in NSW
TS 05492 section 11.8.2 sets the positions, all measured back from the control point:
- End-of-queue marker at the estimated queue length plus 30%. A cone on the shoulder can mark it, and its position goes on the TGS.
- Primary PREPARE TO STOP (T1-18) 1 D before that end of queue. On a two-lane road the first one drivers see goes on both sides; on a multi-lane road every PREPARE TO STOP is duplicated.
- ROADWORK AHEAD (T1-1 or T1-31) no more than 1 D before the primary sign. Where there is a temporary speed zone, the speed signs go 1 D before the primary sign too.
- Repeaters every 120 m between the primary sign and the control point when that distance is over 120 m.
D is the speed of the zone drivers are in before the queue, in metres. Because D lags one zone, a 60 km/h zone that starts just before the PREPARE TO STOP sign still gives D = 80 m if drivers came from an 80 km/h zone.
Drivers should see the end of the queue from at least 2 D on open roads and 1.5 D in built-up areas. On downgrades, high-speed roads, roads with many heavy vehicles, at night or with workers on foot and no barrier, use 1.75 D under 60 km/h and 2.5 D over 60 km/h. If the controller can't see the end of the queue, a second traffic controller must watch it with the bat on SLOW and stay in contact.
NSW end-of-queue risk levels
Table 31 sets the risk rating, which decides how many treatments go on the TGS:
- Level 1, low risk: urban roads with a limit of 70 km/h or less. This is the minimum for TfNSW works. Pick one Level 1 treatment, such as PREPARE TO STOP signs duplicated on both sides and in two locations, or queued traffic warning signs.
- Level 2, medium risk: high-speed urban roads (80 km/h and up) and rural roads and highways from 70 to 100 km/h. Add one Level 2 treatment, such as a VMS, queued traffic signs with flashing lights, rumble strips or a UHF broadcast to heavy vehicles.
- Level 3, high risk: all NSW motorways and the high-risk highways: Newell, Hume, Pacific north of Hexham, Great Western and Princes north of Nowra. Add one Level 3 treatment, such as lane narrowing, police presence, a second advance warning vehicle with VMS or variable speed limit signs.
The rating can be raised for poor sight distance, crash history, gravel roads, no shoulders, many heavy vehicles or slow-moving queues where traffic usually flows freely. The planner lists every treatment so you can pick and record them.
Queensland and WA differences
Queensland measures the primary PREPARE TO STOP from the predicted end of queue using the sight distance in AGTTM Part 3 Table 2.3, which the planner asks you to enter from your TGS. Then:
- if the primary sign is more than 240 m from the controller, add a second PREPARE TO STOP 120 m from the controller
- if it is more than 300 m away, or visibility is lost, consider repeaters no more than 180 m apart (60 m at 55 km/h or less)
- ROADWORK AHEAD or a VMS goes at least 30, 90, 140 or 240 m before the primary sign, or four times the speed above 85 km/h, read at the permanent speed
- above 60 km/h, a 60 km/h zone starts at least one sign spacing before the primary sign
Extra end-of-queue protection is required where the limit is 80 km/h or more and the road carries over 500 vehicles a day, or the sight distance to the end of the queue is less than Table 2.3.
In WA, a PREPARE TO STOP sign is needed when the permanent speed is over 70 km/h or the sight distance to the queue is less than twice the speed limit (open road) or 1.5 times (built-up). Its distance comes from the WA Code of Practice, which the planner doesn't hold yet.
A worked example
This is the example in TS 05492 Tables 29 and 30. A rural 80 km/h road has a portable traffic control device with a 3-minute stopping time. In 15 minutes, 45 light and 6 heavy vehicles arrive northbound.
- Arrivals per minute: 3 light and 0.4 heavy.
- In a 3-minute stop: 9 light and 1.2 heavy, rounded up to 2.
- Queued length: 9 × 8.5 + 2 × 22 = 120.5 m. Plus 30% is 156.7 m, rounded up to 160 m.
With D = 80 m, the primary PREPARE TO STOP goes at 240 m from the control point, ROADWORK AHEAD at 320 m, and one repeater at 120 m. Drivers need to see the end of the queue from 160 m (2 D). A rural road at 80 km/h is Level 2, so the TGS needs one Level 1 and one Level 2 treatment. Southbound, 21 light and 3 heavy vehicles give a 90 m queue, so its primary sign goes at 170 m.
Keep checking on the day
A queue estimate is only a starting point. NSW asks for the queue to be verified on site and monitored through the shift, and a traffic controller may move the PREPARE TO STOP and ROADWORK AHEAD signs under an IMP's direction to keep their distance ahead of a longer queue. Our guides to end of queue management and roadworks queue monitoring cover what to watch for. To lay out the rest of the advance signs, use the sign layout builder, and check the controller position with the sight distance check.
This planner is a planning aid. The queue estimate and treatments belong in the TMP and TGS prepared by a qualified designer, who decides the final layout.