Pedestrian comfort criteria and mapping

Heavily urbanized areas, such as the La Défense district, create regions where winds reach higher speeds, due to the height of the buildings and their high concentration. TheVenturi effect is responsible for these areas of high wind speeds: the cross-section of the wind is reduced by the presence of buildings, so the wind is accelerated. High wind speeds can pose problems for the comfort and safety of building users (using terraces or balconies), but also for pedestrians (or even cyclists) moving through these densely built-up areas. It is therefore legitimate to ask what is the criterion at which wind speed becomes uncomfortable, or even dangerous.

Assessing wind comfort levels

This scale classifies wind force according to speed and the feelings of people potentially exposed to these wind speeds. Force is characterized by a scale ranging from 0 to 12, the Beaufort scale. We don’t present the scale beyond force 9, as it then concerns the most extreme cases (from storms to hurricanes), and most of the scales we’ll present below consider wind to be dangerous from force 8 upwards. All the criteria presented below have the initial aim of ensuring that new urban developments are designed to minimize the negative impacts of wind on the comfort and safety of residents and users. In this way, they guarantee a better quality of life for city dwellers.

Wind comfort criteria

London LDDC criteria

The London criterion, attributed to the London Docklands Development Corporation (LDDC), first appeared in the 1980s. At the time, the rapid development of urban areas, particularly in London, raised growing concerns about living conditions in these densely populated environments. The London criterion was designed to provide standards for urban planning, with particular emphasis on managing the effects of wind. It sets a threshold speed for different areas of activity, as shown in the table below. Not every activity has the same comfort threshold.

For example, a person sitting outside on a bench or terrace is more likely to feel uncomfortable when the wind speed increases than someone on the move (walking, running or even cycling). For very high speeds, the criterion informs us that the wind becomes uncomfortable or dangerous for any type of activity.

All the criteria we present in this article can be read in the same way. Here we describe the London criterion in detail:

Long Seat: speeds exceed 2.5 m/s less than 5% of the time
Short seat: wind speed exceeds 4 m/s less than 5% of the time
Walking at a leisurely pace: speeds in excess of 6 m/s are observed less than 5% of the time
Walking fast: speeds in excess of 8 m/s are felt less than 5% of the time
Uncomfortable: a wind speed of 8 m/s is exceeded 5% or more of the time
Finally, a region is considered hazardous when wind speeds reach 15 m/s with a frequency of at least 0.022%.

For each criterion presented, we show the maps associated with the Courbevoie school project. The map on the left always refers to the project, and the map on the right refers to the baseline (pre-project) or existing state.

Lawson's criteria

The Lawson criterion was first proposed by T.V. Lawson in his 1978 article “The wind content of the built environment” [1]. Like the previous criterion, Lawson’s criterion is based on a threshold according to the activity performed by the user. There are several of these, which we describe below.

Lawson LDDC criterion

The Lawson LDDC criterion indicates a state of comfort in the wind for different activities. Of the three Lawson criteria presented in this article, this is the most widely used.

Outdoor dining: speeds exceeding 2 m/s less than 5% of the time

Seated pedestrian: wind speed exceeds 4 m/s less than 5% of the time
Standing pedestrian: speeds in excess of 6 m/s are observed less than 5% of the time
Walking pedestrian: speeds in excess of 8 m/s are felt less than 5% of the time
Fast running: a wind speed of 10 m/s is exceeded less than 5% of the time
The area is considered uncomfortable when wind speeds exceed 10 m/s more than 5% of the time.

Lawson LDDC criterion

Lawson’s criterion gives other thresholds for the comfort of outdoor activities. It is close to the London LDDC criterion presented above, but with different threshold speed values.

Long Seat: speeds exceeding 1.8 m/s less than 2% of the time.

Short seat: wind speed exceeds 3.6 m/s less than 2% of the time.
Walk quietly: speeds in excess of 5.3 m/s are observed less than 2% of the time.
Walking fast: speeds in excess of 7.6 m/s are felt less than 2% of the time.
Uncomfortable: a wind speed of 7.6 m/s is exceeded 2% or more of the time.

Lawson LDDC criterion

This last Lawson criterion also includes the hazardous nature of certain wind speed values, completing the comfort thresholds.

Sitting: speeds exceeding 4 m/s less than 5% of the time.
Standing: wind speed exceeds 6 m/s less than 5% of the time.
Walking: speeds in excess of 8 m/s are observed less than 5% of the time.

Walking fast: speeds in excess of 10 m/s are felt less than 5% of the time.
Uncomfortable: a wind speed of 10 m/s is exceeded 5% or more of the time.
Unsafe: wind speeds in excess of 15 m/s are reached 0.023% of the time or more.
Dangerous: a wind speed greater than 20 m/s is reached 0.023% of the time or more.

Cartography

For each criterion presented, we show the maps associated with the Courbevoie school project for two of Lawson’s criteria (Lawson LDDC and Lawson).

Industries

Laboratories

Pedestrian comfort criteria and mapping