Lawson 2001
The Lawson 2001 criteria provide a framework for assessing both pedestrian wind comfort and wind safety.
Compared to earlier formulations, Lawson 2001 applies a 5% exceedance probability for comfort categories and introduces explicit safety thresholds for strong winds that could endanger pedestrians.
Lawson 2001 Comfort Categories
| Category | Wind Speed Threshold | Exceedance Probability | Typical Activity | Color |
|---|
| A | ≤ 4 m/s | ≤ 5% | Sitting (cafés, terraces, benches) | |
| B | ≤ 6 m/s | ≤ 5% | Standing / short-term exposure | |
| C | ≤ 8 m/s | ≤ 5% | Strolling / casual walking | |
| D | ≤ 10 m/s | ≤ 5% | Business walking / commuting | |
| E | > 10 m/s | > 5% | Uncomfortable for regular pedestrian use | |
Lawson 2001 Safety Categories
| Safety Class | Wind Speed Threshold | Exceedance Probability | Effect | Color |
|---|
| Safe | ≤ 15 m/s | ≤ 0.023% (~2 hours/year) | Conditions are safe for all pedestrians | |
| S15 – Unsafe (Frail Persons) | > 15 m/s | > 0.023% (~2 hours/year) | Unsafe for vulnerable pedestrians (elderly, children, cyclists) | |
| S20 – Unsafe (All Persons) | > 20 m/s | > 0.023% (~2 hours/year) | Unsafe for the general public | |