Corner Visibility Calculator

Calculator

Example Data Table

Formulas Used

• Sight triangle area: Area = 0.5 × a × b × sin(θ)
• Endpoint distance (between the two leg points): c = √(a² + b² − 2ab cos(θ))
• Stopping sight distance (metric form): SSD = 0.278·V·t + V² / (254·(f ± G))
• Intersection gap sight distance: ISD = 0.278·V·t_gap
• Obstruction inside triangle (using leg distances): (s/a) + (t/b) ≤ 1
• Sight line check (near the critical line): t ≈ b·(1 − s/a), then compare obstruction height to line-of-sight height.

How to Use This Calculator

1. Select units and enter the corner angle for the two legs.
2. Enter the setback distance b from the corner on the minor leg.
3. Choose how a should be set: Manual, SSD, ISD, or Combined.
4. If using speed-based methods, enter speed, reaction time, friction, and grade.
5. Optionally test an obstruction using distances s and t along the legs.
6. Click Calculate. Results appear above the form. Use the export buttons for reports.

Corner Visibility in Construction: Practical Guidance

Corner visibility is a practical safety check for site entrances, road junctions, temporary diversions, and access ramps. The aim is to keep a clear sight triangle so a driver can see approaching traffic in time to stop or merge smoothly. On construction projects, visibility changes as barriers move, stockpiles grow, and equipment parks near corners. This calculator helps you size the clear triangle using three inputs: a known required sight distance, a speed-based stopping distance, or a combined approach.

Start by selecting units and the corner geometry. The intersection angle affects triangle shape: acute corners typically need a longer clear area for the same sight distance, while near‑right angles often require less. Next, choose the sight-distance method. Use Direct when a specification or road authority provides a minimum distance. Use Speed-based when the controlling factor is approach speed and you want an estimated stopping sight distance based on reaction time, friction, and grade. The Combined option takes the larger of direct and speed-based distances for a conservative design.

Example (metric): A site gate meets a haul road at 90°. The driver eye offset from the corner is 4.5 m. Expected speed is 60 km/h, reaction time 2.5 s, friction 0.35, and grade −2% (slight downgrade). The downgrade increases the stopping distance, so the required clear triangle becomes larger than on level ground. If the available clear triangle is shorter than the computed distance, treat it as a hazard and apply controls such as speed reduction, relocating fencing, trimming vegetation, adding a stop line, or assigning a banksman during peak movements.

Use the obstruction check to test whether a specific object sits inside the triangle. Enter distances s and t along the legs and the obstruction height. If the object blocks the line of sight, the calculator flags a potential conflict. Repeat checks for both travel directions and for the most critical vehicle type because eye height and stopping performance vary.

Finally, document your assumptions. Export results to CSV for logs, or create a PDF for safety files and traffic-management documentation. Re-run the calculation when geometry, speed management, or roadside conditions change, and confirm final requirements against local standards and your project plan.

FAQs

1. What is a sight triangle in construction traffic control?

It is the clear area near a corner or exit that must remain free of visual obstructions so drivers can see oncoming traffic and decide to stop, yield, or merge safely.

2. Which sight-distance method should I use?

Use Direct when a standard or specification gives a minimum distance. Use Speed-based when approach speed controls stopping needs. Use Combined when you want the more conservative value between the two.

3. Does a steeper grade change the required distance?

Yes. Downgrades increase stopping distance, so the required sight distance can rise. Upgrades generally reduce stopping distance. Always use realistic grades for the controlling approach direction.

4. How do I model barriers, stockpiles, or parked plant?

Treat them as potential obstructions. If they sit within the triangle and are tall enough to block the line of sight between driver eye height and target height, they should be relocated or reduced.

5. What do driver and target heights represent?

Driver height represents the eye level of the critical vehicle type. Target height represents what must be seen, such as an approaching vehicle, pedestrian, or work-zone sign. Use values consistent with your site vehicles.

6. Why does the corner angle matter?

The angle changes triangle geometry. Acute angles stretch the triangle along the legs, often requiring more clear length for a given sight distance. Obtuse angles generally reduce the required clear length.

7. Is this calculator a substitute for local standards?

No. It is a planning and documentation tool. Always verify results against local road authority guidance, project specifications, and the approved traffic management plan before implementing controls.