The addition of amenities like trees as part of Complete Streets is common and trade-offs are made based on local context. For example, if space constraints limit the ability to plant trees, reducing pavements widths on an excessively wide street provides an opportunity to add a tree belt or planted curb extension. See this 2023 Johns Hopkins study on narrow lanes.
Here are some examples of local programs and policies that reference amenity zones, street trees, etc., in their complete streets policies/programs:
- Arlington Complete Streets Policy (2018) – See 3.4.4 Amenity Zone. It notes “Typically, the minimum width necessary to support standard healthy street tree installation is 6 feet. The City’s Standard Plans allow for narrower tree pitch depth (4.5 feet minimum), but additional rooting space is recommended.” Page 74 (of PDF, not page number) includes a table for street element priorities, including amenity zones.
- Battle Ground Municipal Code Ch. 12.117 – Includes street trees, landscaping, planting strips, and other amenities in their definition of complete streets infrastructure. See Sec. 12.117.040 for information on complete streets infrastructure. (Connell, Wapato and West Richland have similar language in their codes).
- Kenmore Municipal Code Ch. 12.45 – See their policy in Sec. 12.45.020, which notes that street trees and planting strips are a traditional tool.
- Kent Municipal Code Ch. 6.14 – Recommends consulting arborists on designs including street trees.
- Longview Municipal Code Ch. 12.70 – See Sec. 12.70.050, Complete streets infrastructure. It notes trees and landscaping as one of several design features.
- Pacific Municipal Code Ch. 13.26 – See Sec. 13.26.030, Objectives, which includes street trees as a complete streets network objective.
- Renton Municipal Code Sec. 4-6-060 – The Minimum Design Standards Table for Public Streets and Alleys notes that street trees are required per RMC Sec. 4-4-070. F.8 notes that greater sidewalk widths with provisions for street trees and other landscaping may be required in certain areas.
- Tacoma
- GreenRoads – The city became the first GreenRoads Community in 2014. GreenRoads is a rating system for measuring and managing sustainability on infrastructure projects, including streets (see the Sustainable Transport Council’s GreenRoads Rating System).
- Mixed-Use Centers Complete Streets Design Guidelines (2009) – See Amenity Zone standards on pages 37, 41, 47 of the PDF.
- Residential Streets Complete Streets Design Guidelines (2009) – Page 31 of the PDF includes a photo with the note “Planting strips that are a minimum of 6 feet in width accommodate healthy tree growth and provide opportunities for additional landscaping.” See Section 2.3.4, Landscaping and Street Trees.
Stormwater best management practices (BMP), like roadside bioretention/rain gardens and bioswales are another area to look at for guidance (see bioretention section starting on pg. 687 of King County’s 2021 Surface Water Design Manual and Bothell’s Bioswales page). Your city’s stormwater engineer and Ecology can provide guidance on incorporating low impact development (LID) and stormwater BMPs into ROW. This LID presentation from Ecology’s LID guidance page includes reduced road width and changes in road layout and orientation as potential code amendments for implementing LID principles.
Tree planting programs also include standards that may be helpful. Everett provides ROW tree spacing and location guidelines, for example (see Everett’s Right of Way Street Tree Spacing and Location Guidelines (2019)).
And here are a few additional resources:
- Environmental Protection Agency (EPA): Green Streets Handbook (2021) – Includes design considerations for green stormwater practices like bioretention, bioswales, and stormwater planters and tree systems.
- National Association of City Transportation Officials: Complete Streets are Green Streets – Includes user considerations and green stormwater infrastructure benefits and solutions.
- EPA: National Pollutant Discharge Elimination System (NPDES) - Stormwater Best Management Practice, Street Design and Patterns (2021) – Includes siting and design considerations.