How it Helps
Roadside vegetation has the potential to absorb carbon dioxide emissions from vehicles, thus improving air quality and protecting the health of pedestrians, bicyclists, and other vulnerable road users. Vegetation buffers can also intercept and slow runoff by allowing for soil infiltration, thus improving water quality.3 Living green walls can capture excess carbon and influence particulate matter (PM) dispersion.4 Although there is mixed evidence regarding the effectiveness of vegetation barriers to reduce the impact of vehicle emissions, there are enough promising results to warrant additional research.Additionally, vegetation barriers can decrease highway traffic noise while providing other psychological benefits, such as privacy and enhancing urban aesthetics.5 However, the vegetation must be built high and wide, as well as dense, enough to achieve significant noise reductions.
Certain factors must be considered in order for these solutions to be effective, such as the location, height, and density of the vegetation.6 For example, some combination of factors may actually increase near-road pollutant concentrations and worsen air quality.2 Therefore, vegetation barriers must be carefully designed to reduce exposure to vehicle emissions.
Unfortunately, more affluent communities may disproportionately benefit from the provision of roadside vegetation since this solution is often done to improve urban aesthetics simultaneously.7 Underinvested lower-income and minority communities may be less likely to have vegetation barriers and, therefore, be exposed to more vehicle emissions.
1) New York’s High Line
New York City’s elevated park, the High Line, is an innovative urban vegetation design that is shown to reduce pedestrian exposure to both air and noise pollution. Since the park is constructed 25 feet above street traffic, it acts as a buffer between users and vehicle emissions. The High Line has been found to experience approximately 37% less air and noise pollution than the ground-level sidewalk.
2) Superblocks in Barcelona
The city of Barcelona developed a ‘Superblock’ urban design concept, and within each superblock contains green streets that are closed to most vehicular traffic. Therefore, walking and biking are the primary forms of transport, and the areas have experienced improved air quality, less noise pollution, and greater rates of physical activity. Although there was some pushback from the community over implementing these designs, the city council has focused on fostering equality, and the community has since welcomed the positive changes that superblocks have brought.