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Center for Advancing Research in Transportation Emissions, Energy, and Health (CARTEEH)

A USDOT University Transportation Center

Urban Greening

Efforts to increase urban green space—including building new parks, planting trees and shrubs along roadways, introducing community gardens, or installing green roofs or living walls—has the potential to enhance the health of the community and environment while improving urban aesthetics and attractiveness.1 This nature-based solution promotes sustainable city growth and resiliency, and it will require careful planning and engineering practices to be applied.2

Considering this strategy will help achieve the goal of the following objectives

  • Less Contamination
  • Less Emissions
  • Less Traffic Noise
  • Connectivity and Inclusion
  • Healthy Destinations
  • Less Traffic Violence
  • Active Transportation
  • Green Space

Transportation lifecycle phases

This strategy is associated with the following transportation lifecycle phases:

  • Construction
  • End of Life
  • Maintenance
  • Material Selection
  • Operations
  • Policy and Planning
  • Project Development

Who's involved

  • Local governments
  • MPOs
  • Policymakers
  • Private developers
  • Vegetation management experts
Efforts to increase urban green space—including building new parks, planting trees and shrubs along roadways, introducing community gardens, or installing green roofs or living walls—has the potential to enhance the health of the community and environment while improving urban aesthetics and attractiveness.1  This nature-based solution promotes sustainable city growth and resiliency, and it will require careful planning and engineering practices to be applied.2

How it Helps

There are many positive health outcomes associated with urban greenery, such as improved mental health, lowered stress levels, greater physical activity levels, longer life expectancy, reduced air and noise pollution, and other benefits.3 For example, the presence of street trees may reduce the incidence of childhood asthma, either through encouraging more outdoor activities or improving local air quality.4 Additionally, greenery can absorb excess rainwater and reduce run-off in low-lying areas.5 Green space can also improve social cohesion by connecting communities together, providing recreational activities, and reducing loneliness.6
Urban green space can improve air quality since vegetation has the ability to sequester excess carbon in the air and offset carbon emissions. Vegetation can also reduce runoff and flooding potential by absorbing rainwater and other nutrients. Plants can also mitigate the urban heat island effect, or the phenomenon that occurs when cities experience higher temperatures due to heat-retaining surfaces such as concrete roads.7 Therefore, plants have a cooling ability through providing shade and releasing moisture into the air.8
Placing greenery on the sides of streets can also serve as a traffic calming device since it can reduce the width of the street and discourage speeding.9 Therefore, lining sidewalks with trees and shrubs can encourage more community members to bike or walk to their destinations due to enhanced attractiveness and perceived sense of safety.
Overall, nature-based solutions like urban greenery can combat the effects of climate change, increase property values in residential and commercial areas, and promote public health.2

Implementing

Design & Accessibility:

When planning the design and location of urban green space, city planners should have clear objectives and long-term goals. This can include how planners want the space to be utilized and which populations they want to serve. Additionally, green space should be placed in close proximity to urban residents with sufficient signage, safety features, and infrastructure features to serve all population groups.

Potential Barriers:

There are some potential barriers to using green space.6 For example, some communities might not have the proper sidewalk or public transit infrastructure to get to urban green spaces if it is not close by. A lack of benches could be another barrier preventing some groups of people from utilizing green space. Additionally, fears related to racism or other forms of discrimination can prevent people from using green space.

Management & Maintenance:

Planners will need to establish transparency regarding who is responsible for the management and maintenance of the urban green space. The city should communicate frequently with vegetation management experts as well as the city’s parks and recreation department to determine safe plant species and apply the best ecological maintenance practices.

Collaboration & Community Involvement:

City planners should engage in multi-sectoral collaboration with local businesses, transportation planners, environmental groups, health departments, community members, other stakeholders when implementing urban green space. This will help ensure that the green space is meeting local needs and will be effective in the future. Additionally, the promotion of urban green space will increase the use and acceptability of the space.

Equity Concerns:

Unfortunately, the distribution of urban green space is an environmental justice issue, with many minority communities having less access to urban green space than more affluent communities.10 For example, studies have shown that there is an unequal distribution of street trees in certain neighborhoods, particularly where there is a higher proportion of African Americans and low-income individuals.11 Additionally, the creation of new urban green space can lead to gentrification other equity issues from rising property values in poorer areas. Therefore, planners need to be careful that green space is readily available in these communities, and it is at the same quality as the green space in more affluent neighborhoods.

Examples

1) Urban Greening Factor (UGF) London Plan Guidance

London’s Urban Greening Factor (UGF) Guidance requires that all major development projects to incorporate urban greenery in their design plans. The goal of this is to increase green coverage in London’s built environment and advance the health of the city.

https://www.london.gov.uk/what-we-do/environment/parks-green-spaces-and-biodiversity/urban-greening

2) Santa Fe, New Mexico Guidebook for Green Infrastructure

The City of Santa Fe has developed a project process for incorporating green infrastructure into roadway projects and long-term city planning. The city has developed a guidebook that explains design considerations, maintenance practices, and regulatory considerations for the implementation of green infrastructure.

https://www.santafenm.gov/media/archive_center/Santa_Fe_GI_Guidebook_for_Road_Projects_10092019.pdf

1. Haase, D., et al. (2017). Greening cities—To be socially inclusive? About the alleged paradox of society and ecology in cities. Habitat International, 64, 41-48. https://doi.org/10.1016/j.habitatint.2017.04.005
2. FEMA. (2023). Nature-Based Solutions. https://www.fema.gov/emergency-managers/risk-management/nature-based-solutions
3. Nieuwenhuijsen, M. (2020). Urban and transport pathways to carbon neutral, liveable and healthy cities; A review of the current evidence. Environment International, 140. https://doi.org/10.1016/j.envint.2020.105661
4. Lovasi, G. S., et al. (2007). Children living in areas with more street trees have lower prevalence of asthma. Journal of Epidemiology & Community Health, 62(7). https://doi.org/10.1136/jech.2007.071894
5. The Fourth Regional Plan. On city streets, prioritize people over cars. http://fourthplan.org/action/streets-for-people
6. Ridgley, H. (2020). Improving access to greenspace: A new review for 2020. Public Health England. https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/904439/Improving_access_to_greenspace_2020_review.pdf
7. Alberro, H. (2019). Urban greening can save species, cool warming cities, and make us happy. The Conversation. https://theconversation.com/urban-greening-can-save-species-cool-warming-cities-and-make-us-happy-116000
8. EPA. (2023). Reduce Urban Heat Island Effect. https://www.epa.gov/green-infrastructure/reduce-urban-heat-island-effect
9. ANS Global. The Importance of Urban Greening. https://www.ansgroupglobal.com/blog/importance-urban-greening
10. Wolch, J. R., et al. (2014). Urban green space, public health, and environmental justice: The challenge of making cities 'just green enough'. Landscape and Urban Planning, 125, 234-244. https://doi.org/10.1016/j.landurbplan.2014.01.017
11. Landry, S. M., et al. (2009). Street Trees and Equity: Evaluating the Spatial Distribution of an Urban Amenity. Environment and Planning A: Economy and Space, 41(11). https://doi.org/10.1068/a41236