Rear-end crashes into stopped traffic are one of the biggest risks at a stop/slow or portable traffic signal site. The defence is knowing, before you set up, how far back the queue will reach, and putting the warning signs beyond it. The Queensland Guide to Temporary Traffic Management (QGTTM) Part 3 sets out how to estimate that end-of-queue position. This guide walks through the method step by step, with a worked example, and shows a calculator that does it from TMR's traffic counts.
Why the end of queue matters
Drivers approaching a traffic control station expect to see a PREPARE TO STOP sign and then a controller or signals. What they don't expect is a line of stopped cars well before that, beyond the last warning sign. QGTTM Part 3 Section 4.8 (which replaces the advance warning area section of Austroads' AGTTM Part 3 in Queensland) therefore asks the traffic management designer to estimate an end-of-queue position for the approach to each traffic control station, and to design the advance warning area from there rather than from the controller.
The estimate is based on the maximum expected traffic flow on that approach during the hours the traffic control will run, and on the maximum stopping time.
Step 1: the maximum stopping time
The maximum stopping time is the longest that queued traffic will be held at a station: from when the controller stops traffic until the same controller releases it again. QGTTM lists what it typically includes:
- the time for the queue from one approach to pass the station and travel the length of the closure;
- the time for the queue at the other end to leave its station and travel the closure (at the same time, or after the first queue in a shuttle-flow arrangement);
- any hold time when no traffic is moving through the site;
- a margin for vehicles travelling the closure below the signed speed;
- with more than two stations, the time for each queue to be released and travel through.
As a rough guide, a 1 km closure at 40 km/h takes about 90 seconds to drive, so two queues in shuttle flow plus a little hold time quickly add up to five minutes or more.
Step 2: the five-minute count
The method works on the number of average vehicles and heavy vehicles arriving at the station in five minutes. QGTTM gives three ways to get it, in order of preference:
- An actual five-minute count during the busiest time the site will be occupied, of the traffic approaching that station only (not both directions added together).
- AADT with hourly breakdowns and heavy-vehicle percentage: take the busiest hour during the works, divide it by 12 for a five-minute figure (and by two if the figure is for both directions), then split it into heavy and other vehicles using the heavy-vehicle percentage.
- AADT alone: divide the AADT by 10 for an hourly figure, then by 12, halving it for a two-way figure, and apply the heavy-vehicle percentage.
TMR publishes AADT, heavy-vehicle percentages and average traffic by hour of the day for its count sites on the Queensland Open Data Portal. See what AADT means and how to read TMR's counts.
Step 3: Table 4.3 and the queue length
Table 4.3 turns the five-minute count into metres of queue. It assumes an average vehicle takes up 6 m and a heavy (or oversized) vehicle 20 m for a five-minute stop, and scales the multipliers for other stopping times:
| Maximum stopping time | Ma (per average vehicle) | Mo (per heavy or oversized vehicle) |
|---|---|---|
| 2 minutes | 2.4 | 8 |
| 5 minutes | 6 | 20 |
| 10 minutes | 12 | 40 |
| 15 minutes | 18 | 60 |
| 30 minutes (unusual) | 36 | 120 |
The estimated queue is the number of average vehicles times Ma, plus the number of heavy vehicles times Mo. Two rules apply: part vehicles are rounded up, and the queue is never less than one average vehicle plus one heavy vehicle. Where very long vehicles are common, as on mining and outback routes or where most vehicles tow, use an average length that matches the real traffic.
A worked example
TMR's Technical Note TN195 includes an example with 12 average vehicles and one heavy vehicle counted in five minutes, and a 10-minute maximum stopping time. From the table, Ma is 12 and Mo is 40, so the estimated queue is 12 × 12 + 1 × 40 = 184 m.
Step 4: placing the advance warning signs
With the queue estimated, the advance warning area is built back from the end of the queue:
- End of queue: the queue starts at the STOP HERE sign, 6 m before the controller or portable traffic control device, so the end of queue is 6 m plus the queue length from the station. QGTTM suggests a cone or bollard on the shoulder there, so the controller can see when the queue reaches it.
- Primary PREPARE TO STOP: at least the AGTTM Table 2.3 distance before the end of queue, not before the controller. That distance is 50 m at 45 km/h or less, 70 m at 46–55 km/h, 90 m at 56–65 km/h and twice the speed above that.
- Additional PREPARE TO STOP: where the primary sign is more than 240 m from the controller, another one 120 m from the controller, to protect the controller.
- Repeaters: where it's more than 300 m away or visibility is lost, consider repeater PREPARE TO STOP signs, no more than 60 m apart at 55 km/h or less and 180 m apart above that (Table 4.4(a)).
- ROADWORK AHEAD or a VMS: a Table 4.4(b) distance before the primary PREPARE TO STOP, based on the road's permanent speed: 30 m up to 55 km/h, 90 m at 56–65, 140 m at 66–75, 240 m at 76–85, and four times the speed in metres above that.
- Speed zone: where the approach speed is over 60 km/h, a 60 km/h zone must start at least one sign spacing before the primary PREPARE TO STOP.
In the worked example at 60 km/h, the end of queue is 190 m from the controller and the primary PREPARE TO STOP 280 m (6 + 184 + 90), so an additional PREPARE TO STOP goes at 120 m. QGTTM Part 3 also covers intersections within the advance warning area and queuing in two lanes; check those sections for your site.
Monitor the queue. Traffic surges happen. If the queue approaches the marked end-of-queue position, the controller tells the site supervisor, timings can be adjusted to favour the longer queue, and a pre-designed contingency plan is put in place; without one, the traffic management designer must be contacted urgently.
Calculating it from TMR's counts
Chainage includes a queue calculator based on this method. Look up a point on a state-controlled road, tap the traffic figure to open the TMR count site behind it, and enter the maximum stopping time. For each approach it takes the busiest hour from the site's hourly counts (scaled up where traffic has grown since they were counted), divides by 12, splits it by that direction's heavy-vehicle share, applies Table 4.3 with the rounding and minimum rules, and lists the end of queue and the distances to the PREPARE TO STOP, repeater, speed zone and ROADWORK AHEAD signs. A chart shows the queue for every hour of the day, so you can see the quieter times to work.
It's an aid for the traffic management designer, not a substitute: where you can, check it against a real five-minute count at the busiest time, and check sight distance and side roads on site.
Frequently asked questions
What is the queue length formula in QGTTM Part 3?
Queue length = (average vehicles in five minutes × Ma) + (heavy vehicles in five minutes × Mo), with Ma and Mo from Table 4.3 for the maximum stopping time: for example 12 and 40 for ten minutes. Part vehicles are rounded up, and the minimum is one average vehicle plus one heavy vehicle.
Do I count both directions?
No. The five-minute count is for the traffic approaching the station you're designing for. If you're working from a two-way AADT, halve it; better still, use the directional counts TMR publishes for each count site.
Where does the PREPARE TO STOP sign go?
The primary PREPARE TO STOP goes a minimum distance before the predicted end of queue (90 m at 60 km/h), not before the controller. If it ends up more than 240 m from the controller, an additional sign goes 120 m from the controller.
What if the stopping time isn't in Table 4.3?
The multipliers are proportional to the stopping time: 1.2 m per minute for an average vehicle and 4 m per minute for a heavy vehicle, so they can be worked out for any stopping time. A longer stopping time gives a longer queue.
Is QGTTM the same as AGTTM?
QGTTM is TMR's Queensland supplement to the Austroads Guide to Temporary Traffic Management. Each part follows the matching AGTTM part and sets out the Queensland differences and additions, such as the replacement Section 4.8 on the advance warning area.
Sources
- Queensland Department of Transport and Main Roads, Queensland Guide to Temporary Traffic Management Part 3: Static Worksites (November 2025), Section 4.8, Tables 4.3 and 4.4.
- TMR, Technical Note TN195: Traffic Guidance Scheme worked examples (December 2021).
- Austroads, Guide to Temporary Traffic Management Part 7: Traffic Controllers, Table 2.3.
- Austroads, Guide to Temporary Traffic Management Part 3: Static Worksites.
- Queensland Government Open Data Portal, Queensland traffic data averaged by hour of day and day of week.