Streets that incorporate different types of vegetation and permeable surfaces to filter and cleanse storm water run-off are known as “green streets.” Green streets offer a variety of environmental benefits, including improving water quality, reducing greenhouse gas emissions through carbon absorption, and reducing urban heat island effects. In Analysis of the Benefits of Green Streets, Mineta Transportation Institute (MTI) researchers calculated green street infrastructure benefits to help determine the most effective methods in the fight against climate change.
Green street elements—such as trees—absorb carbon dioxide and other pollutants from the air, reducing the costs of future climate change mitigations and medical care from conditions such as asthma, which are worsened by such pollutants. To measure potential benefits of green street infrastructure, the team initially considered 14 calculators, such as the Greenhouse Gas Equivalency Calculator and Water Quality Index Calculator. Ultimately, with input from Caltrans about case study sites, researchers used two calculators to evaluate in depth: i-Tree Design and Landis Pedestrian Level of Service (PLOS).
I-Tree Design is an online calculator created by the U.S. Forest Service to allow simple estimations of benefits provided by trees, based on input such as tree location, species, and size. The PLOS was used as a basis for the development of the 2010 version of the Highway Capacity Manuel’s (HCM’s) multimodal level of service and includes two components that calculate the level of service grades for pedestrians and bicycles, assigning a letter grade— “A” through “F”— based on input such as geometric and traffic characteristics.
Researchers tested these two calculators using hypothetical “before” conditions on 11 green street case study sites, with “before” conditions based on the removal of all green street infrastructure elements at each site.
Key findings from i-Tree Design include:
Overall, researchers conclude the i-Tree Design’s sensitivity to a range of environmental characteristics, ease of use, and scalability make it a promising candidate to serve as a common frame of reference and analysis for Caltrans and other agencies. Similarly, the Landis PLOS method could be useful in green street measurement and is already used as a standard in the industry.
“The use of these calculators can spread awareness and appreciation of green streets’ benefits and advance the fight against harmful climate change,” says report author Dr. Chris Ferrell.
ABOUT THE MINETA TRANSPORTATION INSTITUTE
At the Mineta Transportation Institute (MTI) at San Jose State University (SJSU) our mission is to increase mobility for all by improving the safety, efficiency, accessibility, and convenience of our nations’ transportation system. Through research, education, workforce development and technology transfer, we help create a connected world. MTI was founded in 1991 and is funded through the US Departments of Transportation and Homeland Security, the California Department of Transportation, and public and private grants. MTI is affiliated with SJSU’s Lucas College and Graduate School of Business.
ABOUT THE AUTHORS
Dr. Christopher Ferrell is an MTI Research Associate and Principal and Executive Director at Transportation Choices for Sustainable Communities. John M. Eells is a transportation planner with 42 years of experience, Dr. Richard W. Lee is an MTI Research Associate and lecturer at the Department of Urban and Regional Planning at San Jose State, and Reyhane Hosseinzade, is an MTI Research Assistant and a transit service planner at Valley Transportation Authority.
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