Speed Limit Compliance Calculator

Example Data Table

A small sample of readings for a 20 km/h worksite limit with 2 km/h tolerance.

Formula Used

• Allowed maximum speed = Speed limit + Tolerance
• Compliance rate (%) = (Compliant readings ÷ Total readings) × 100
• Over-limit rate (%) = (Over-limit readings ÷ Total readings) × 100
• Average speed = (Sum of readings ÷ Total readings)
• Trip-derived speed = Distance ÷ Time (converted to your unit)
• 85th percentile uses sorted readings and linear interpolation
• Overspeed severity index = Average amount above allowed max, only for over-limit readings

Compliance can be improved by adjusting signage placement, adding spot checks, and tuning haul-road design where high-percentile speeds persist.

How to Use This Calculator

1. Select the unit system you use onsite.
2. Enter the posted speed limit and any permitted tolerance.
3. Add one zone/area and pick the shift for comparison.
4. Paste speed readings from radar, telematics, or logs.
5. Optionally enter distance and time to derive one speed.
6. Click Calculate to view compliance and percentile metrics.
7. Download CSV or PDF for records, audits, and coaching.

Professional Guidance Article

1) Why speed compliance matters on active sites

Speed is a leading contributor to struck-by incidents, rollovers, and near-misses on busy projects. Even a small increase in vehicle speed raises stopping distance and reduces reaction time for pedestrians and equipment operators. A practical program focuses on observable behavior and repeatable metrics.

2) Typical speed limits and zone setting

Many contractors use lower limits near work fronts, gates, and pedestrian crossings, then slightly higher limits on controlled haul roads. Common site ranges are 10–25 km/h (or 5–15 mph), but your layout, visibility, and traffic mix should drive the final number. Document zones clearly in your plan.

3) Using tolerance correctly

Tolerance is not a “free pass.” It is a practical buffer to account for device accuracy and rounding. Keep it small and consistent, such as 1–3 km/h (or 1–2 mph), and apply it only to compliance scoring. Continue coaching operators to stay at or below the posted limit.

4) What the compliance rate tells you

The compliance rate is the percentage of readings at or below the allowed maximum. Many teams aim for 90–95% compliance in controlled areas. Track the rate by zone and shift to identify patterns, then focus improvements where the rate is consistently lower than your target.

5) Why the 85th percentile is useful

The 85th percentile shows how fast most traffic is moving, not just the average. If the percentile remains above the allowed maximum, signage alone may be insufficient. Consider engineering controls such as chicanes, speed humps, narrowed entries, or improved separation between people and vehicles.

6) Overspeed severity and corrective actions

The overspeed severity index estimates the average amount above the allowed maximum for over-limit readings. A low overspeed rate with high severity can indicate a small group of high-risk drivers. Pair coaching with progressive discipline, and confirm improvements with follow-up sampling in the same zone.

7) Data collection tips for reliable results

Use consistent observation windows, such as a 30–60 minute spot check at peak traffic times. Capture at least 20–50 readings per zone when possible, and note weather, visibility, and congestion. Combine radar checks with telematics where available to validate trends and reduce bias.

8) Reporting, audits, and continuous improvement

Export CSV for trend charts and PDF for formal records. Review results during toolbox talks and supervisor meetings, then set clear actions: update signage, adjust traffic routes, schedule targeted spot checks, and recognize improvement. Repeat monthly or after major layout changes for stronger control.

FAQs

1) How many readings should I enter?

Use enough observations to represent normal traffic. A practical minimum is 20 readings per zone, while 50 or more improves confidence when shifts and vehicle types vary.

2) Should I use km/h or mph?

Use the unit system your site signs and policies use. The key is consistency across the limit, tolerance, and all readings, so the compliance scoring is correct.

3) What does the risk band mean?

It is a simple indicator based on compliance and the 85th percentile. “Low” suggests strong control, “Moderate” flags improvement opportunities, and “High” signals urgent review of controls and supervision.

4) Can I calculate compliance from distance and time?

Yes. If you only have a timed run, enter distance and time to generate one speed. For better insight, add multiple readings from radar or telematics.

5) Why is the 85th percentile higher than the average?

Because it reflects faster drivers in the distribution. The average can look acceptable even when a sizable group regularly exceeds the allowed maximum.

6) How do I set a reasonable tolerance?

Keep tolerance tight and aligned with measurement accuracy and policy. Many sites use 1–3 km/h or 1–2 mph, then coach to the posted limit rather than the tolerance.

7) What should I do if overspeed severity stays high?

Prioritize engineering controls and supervision in that zone. Combine route changes, physical calming measures, and targeted coaching. Re-measure after changes to confirm the severity index drops.