Greenroads Certified Silver

25th Street Pedestrian and Bicycle Improvements



This project will involve the design and construction of porous bike lanes, sidewalk, and shared path, an LID stormwater treatment/retention facility, LED lighting, ADA facilities, and a warm mix asphalt overlay of 25th Street between Bill McDonald Parkway and Douglas Ave.

Actual Cost: $1,345,922.71 USD

Engineer's Estimate: $1,389,658.00 USD

Lowest Bidder: $1,235,413.76 USD

Length: 0.22 mi (0.44 lane miles)

Funders/Stakeholders: Local Transportation Benefit District

Owner: City of Bellingham, WA

Lead Design: Tuttle Engineering and Management

Design Support: Osborn Consulting, Rubenkonig Planning and Landscape Architecture

Contractor: Faber Construction

Functional Class: Collector

Greenroads Version: 1.5


This project improves bike, pedestrian, and transit facilities along existing roadways, provides stormwater detention and treatment, improves, and enhances safety.


A strong materials management strategy helped this project earn major points and substantially reduce their environmental impacts due to construction, earning more points for materials than any project to date.

  • Warm-mix asphalt and 70.7% reclaimed materials content in pavement base reduced energy footprint by approximately 18%
  • Reduced CO2e footprint by approximately 15%
  • 89% reuse of existing pavement structure in place helped minimize construction costs
  • Bike, pedestrian and transit accessibility improvements throughout the corridor
  • Energy efficient LED street lighting
  • Porous concrete sidewalk helped to offset flow control requirements and meet treatment goals
  • Bioinfiltration basin designed to manage stormwater quantities from on-site and off-site, including future planned development
  • Native, non-invasive vegetation that does not require irrigation cleans and filters stormwater


The design team employed what is considered an approved "treatment trade" by the Washington Department of Ecology, where a stormwater BMP is designed to be bigger in order to accommodate an alternate or additional offsite area because site constraints (such as existing system capacity, right of way space, soil permeability, groundwater conditions, or topography to name a few) make it difficult and (sometimes) infeasible to meet minimum treatment or capacity requirements using low impact development (LID). This design approach is a creative way to meet compliance requirements for quantity of water managed and treatment goals, and ultimately satisfies state regulatory minimums for quality treatment and quantity. However, this approach does not meet Greenroads treatment performance requirements for the street itself, despite the giant stormwater basin that was installed with all good intentions and legally. Why?

It is an important lesson in the difference between "compliance" which is measured by permitting agencies, and often discounts existing conditions by allowing them to stay as-is, and "performance" which is measured by Greenroads Certification in the as-built condition and considers the whole project area (not just new or changed surfaces).

In the case of 25th Street, the site drainage pattern (you can see this in person and on the construction drawings) shows that a majority of the stormwater that falls on 25th Street and at the updated intersections drains into existing storm sewers and does not actually flow through and receive treatment in the huge basin that was installed. This means the project earns credit for EW-2 Runoff Flow Control, because the existing systems plus the new basin manage all of the expected volumes in some way. The volumes of water that do drain into the basin come from mostly uphill and the surrounding development areas on the north/high end of the project. The project was able to earn all 3 points for Runoff Flow Control due to the area of the basins that influenced the design being much larger than the project area itself, including three large subbasins in the surrounding watershed.

However, for runoff treatment, the volume of surface water that falls within the project area itself that flows into the new basin from within the project boundary is somewhere between 55-60% by volume, with the remainder flowing untreated into conventional storm systems at the south side of the project. All of the water that does flow into the basin is treated to an enhanced level (91% of 55-60% plus the run-on volumes from adjacent basins amounting to almost twice that of the project itself). Traditional stormwater systems do not provide pre-treatment only if they are not retrofit, therefore, EW-3 Runoff Quality was not earned, since the minimum treatment volume for EW-3 of 90% of on-site runoff was not met.

In case you are wondering, why is the infiltration basin so big? Two reasons it is such an impressive stormwater BMP:

  1. The soil conditions were not great for infiltration, so it takes longer to drain a large amount of water, and the street has quite a slope so it needed substantial weirs too, and 
  2. It is mostly designed for the future, considering potential site runoff from roofs and new pavement areas. It is likely that the new stormwater basin will not be completely full until the nearby planned development occurs, which is the main intent of the treatment trade. 
This approach will allow the City to avoid constructing new underground stormwater utility infrastructure, and avoid that substantial capital cost, once that development is built.

A giant infiltration basin complete with concrete weirs was part of the stormwater management strategy for 25th Street.

25th Street Ped Bike Improvements Project used warm mix asphalt.

Before - 25th Street facing SB

New bioinfiltration basin on 25th Street looking southbound.

Porous concrete sidewalk on 25th Street

Porous concrete sidewalk on 25th Street meanders along the large bioinfiltration basin.

Before - 25th Street facing NB toward WWU

A new winding sidewalk complete with ADA accessible ramps and stairway provided needed pedestrian connectivity to the University on 25th Street.