The Lawson Pedestrian Wind Criteria is a globally-accepted standard used to assess wind impacts on pedestrian safety and comfort. In general, strong winds and wind gusts can negatively impact the pedestrian experience and may even pose a safety risk.
Pedestrian Wind Comfort Criteria aim to classify different areas by the activities pedestrians may tolerate under predicted wind conditions. In essence, pedestrians can tolerate different strengths of wind depending on their activity. A runner, for instance, may tolerate or even enjoy a moderate breeze; on the other hand, diners enjoying a meal on a patio may find that those same winds detract from their dining experience.
Orbital Stack uses a Lawson Comfort Criteria scale that is a comprehensive amalgamation of both the LDDC Lawson Comfort Criteria scale mentioned above and the modified version of the Lawson LDDC criteria referred to as the City Lawson Criteria developed by the City of London, which can be explored further at this link: Wind Microclimate Guidelines.
The Lawson Criteria characterizes wind conditions by the Gust Equivalent Mean (GEM), an adjusted wind speed calculated from average hourly wind speeds (steady-state) and wind gusts (spontaneous). These speeds are based on an analysis of all 24 hours of the day across all four seasons. Comfort categories are defined such that the GEM must remain below the category threshold at least 95% of the time (see table below).
| Activity | Description | GEM Speed (mph) | GEM Speed (kph) | GEM Speed (m/s) | LDDC Lawson Category | City Lawson Criteria Category |
|---|---|---|---|---|---|---|
| Frequent Sitting | Little to no breeze. Acceptable for frequent outdoor sitting use such as a restaurant or café patio. | ≤ 5.5 | ≤ 9 | ≤ 2.5 | Sitting | Frequent Sitting |
| Occasional Sitting | Calm or light breezes. Acceptable for occasional outdoor seating, such as public outdoor spaces, balconies and terraces intended for occasional use. | ≤ 9 | ≤ 14.5 | ≤ 4 | Sitting | Occassional Sitting |
| Standing | Gentle breezes. Acceptable for building entrances, bus stops, and other places where pedestrians may linger. | ≤ 13.5 | ≤ 21.5 | ≤ 6 | Standing | Standing |
| Leisurely Walking | Moderate winds. Acceptable for window shopping or leisurely strolls across a park or plaza. | ≤ 18 | ≤ 29 | ≤ 8 | Leisurely Walking | Walking |
| Fast Walking | Relatively strong winds. Tolerable for brisk walking, jogging or cycling. | ≤ 22 | ≤ 36 | ≤ 10 | Uncomfortable | Uncomfortable |
| Uncomfortable | Too windy for any normal pedestrian activities. A more in-depth wind analysis study might be necessary. | > 22 | > 36 | > 10 | Uncomfortable | Uncomfortable |
Analysis Criteria – Supplemental Information
- Hours of the Day: All
- Seasons: All
- Allowed Exceedance (Comfort): 5%
- Allowed Exceedance (Safety): 0.022%
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