Lawson LDDC - “City Lawson” Criteria
The Lawson LDDC criteria were developed during the London Docklands redevelopment in the 1980s and have since been adopted (with modifications) by the City of London as the standard for wind assessments in that area.
This variant of Lawson’s criteria uses a 5% exceedance probability for comfort and applies a single conservative safety threshold. The intention was to balance pedestrian comfort with the City’s ambition to encourage active, lively public spaces.
Lawson LDDC Comfort Categories
| Category | Wind Speed Threshold | Exceedance Probability | Typical Activity | Color |
|---|---|---|---|---|
| A | ≤ 2.5 m/s | ≤ 5% | Frequent sitting (cafés, terraces) | |
| B | ≤ 4 m/s | ≤ 5% | Occasional sitting (benches, short stays) | |
| C | ≤ 6 m/s | ≤ 5% | Standing / entrances / queuing | |
| D | ≤ 8 m/s | ≤ 5% | Walking / transit areas | |
| E | > 8 m/s | > 5% | Uncomfortable for regular use |
Lawson LDDC Safety Criterion
| Safety Class | Wind Speed Threshold | Exceedance Probability | Effect | Color |
|---|---|---|---|---|
| Unsafe (All Persons) | > 15 m/s | > 0.022% (~2 hours/year) | Unsafe for pedestrians and cyclists; mitigation required |