Pavements & traffic · Traffic management & parking
Lane closure: tapers, buffer, signs and queue (TTM) calculator
Single-lane closure on a multilane road. The merge and shoulder taper lengths follow from the approach speed and lane width, the longitudinal buffer from the stopping sight distance, and the advance-sign spacing and number of delineating devices are given. The remaining lanes' work-zone capacity is compared with the hourly demand; if demand exceeds capacity the queue grows at the difference, giving the queue length and worst delay over the closure.
Standard: Austroads Guide to Temporary Traffic Management (AGTTM) Part 3 concepts · AS 1742.3 · taper L = W·S²/155 (≤ 60 km/h), W·S/1.6 (≥ 70 km/h) · deterministic queueing
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Inputs in the worked example
The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.
| Input | Value | Unit |
|---|---|---|
| Approach (posted) speed | 80 | km/h |
| Work-zone speed | 60 | km/h |
| Lane width closed | 3.5 | m |
| Lanes in the direction | 2 | |
| Lanes closed | 1 | |
| Hourly demand (one direction) | 1300 | veh/h |
| Work-zone capacity per open lane | 1500 | veh/h/ln |
| Heavy vehicles | 8 | % |
| Duration of the closure | 3 | h |
| Work area length | 120 | m |
| Advance sign spacing (0 = guide by speed) | 0 | m |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Merge taper length | 175 | m |
| Shoulder taper (L/3) | 58 | m |
| Longitudinal buffer (SSD at work-zone speed) | 73 | m |
| Advance warning sign spacing | 120 | m |
| Delineating devices (taper @ 12 m, tangents wider) | 23 | |
| Work-zone capacity | 1,442 | veh/h |
| Demand / capacity | 0.90 | |
| Queue at the end of the closure | 0 veh (0 m) | |
| Worst delay | 0.0 | min |
- ✓ Demand within work-zone capacity (no queue) — 90 %
- ✓ Queue shorter than 1 km — 0 m
- ✓ Speed reduction ≤ 30 km/h through the work zone
Method, formulas and assumptions
- Taper L = W·S²/155 for S ≤ 60 km/h and W·S/1.6 for higher speeds (metric MUTCD form); AGTTM and the state road authority's tables govern the traffic guidance scheme.
- Buffer = stopping distance at the work-zone speed (RT 2 s, d = 0.36). Sign spacing guide: 30 m (≤ 50 km/h), 60 m (≤ 70), 120 m (≤ 90), 200 m above.
- Capacity of open lanes = lanes × capacity per lane ÷ (1 + 0.5·HV); queue grows at demand − capacity (deterministic queueing), 7.5 m per vehicle shared over the approach lanes.
- A traffic guidance scheme must be prepared by an accredited person (AGTTM / state requirements).
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.