Street trees work best if wind is not too strong, yet enough ventilation is allowed. Wind turbulence is limited to above the tree canopy in narrow streets, while ventilating air flows through the tree canopies. Porosity of the canopy should be more than 40% to allow trees to function optimally as air filters.
Street layout using green elements to improve air quality must be designed on a site-specific basis. The size of the trees, the distance from and height of adjacent buildings and the porosity of the trees all affect the capacity of the design to improve the experience at street level.
If there is not enough room in the street profile for trees, use other methods such as hedges, green roofs, green walls (min. 5-7m high) and pergola structures with green to perform air filtering and/or ventilation functions. Groundcover plants also capture particulate matter at pedestrian level. Natural, uneven, extensively maintained plant mixes are more effective than mown lawn.
Integrate green solutions for storm water management within the street’s pattern of traffic flow by reducing unnecessary impervious surfaces and replacing them with green swales, pavement planters and green curb extensions. This helps reduce the stress on storm sewer systems and adds to the aesthetics of the street.
Plant green along the street so it is functional, aesthetic and does not hinder the flow of traffic.
In new development:
Include enough room for green in the planning of infrastructure in order to optimize the effects on the air quality, wind and water runoff. 20% of the infrastructure surface should be reserved for green.
In existing development:
Determine whether existing trees help or hinder the air quality of the street and adjust the design to provide optimal functioning of the trees and other green layers. Check the availability of space for green, as well as the traffic safety regulations.