These three designs comprise about 90% of ODOT’s interchanges. We developed examples to delineate the average total acres of pervious area associated with each design. That data provided us with an initial estimate of more than 90% of interchange acreage statewide owned by ODOT.
Our research allowed us to estimate total interchange area of 21,369 acres. Of that, an estimated 12,701 acres of pervious area is available for stormwater management. This is a significant amount, especially considering increasing land prices. These numbers also emphasize the importance of taking advantage of what the agency already owns.
Next Page: 11 potential constraints
11 potential constraints
As transportation departments explore the potential of BMP retrofits, it’s important to also identify possible implementation obstacles so they can be addressed proactively rather than reactively.
Federal Highway Administration (FHWA)/ODOT policyon interchange infield usage: New policies or policy updates could restrict development.
Utilities: Particularly in urban areas, existing utilities like power lines could limit digging and, thereby, construction of bioswales and other structures.
Previously placed fill material or old pavement sections: If waste areas for previous projects already exist, it may not be worth the costs associated with removal and disposal.
Compaction of fill areas: In the areas described above, infiltration and permeability could be limited.
Slope stability: Terrain could make it difficult to dig and construct a BMP.
Safety: It will be essential to design BMPs to reduce standing water, which by attracting wildlife like deer and birds, creates dangerous driving circumstances.
Maintenance: During road repair, a BMP could present obstructions and complications while making it difficult to keep traffic moving.
Lack of understanding: A basic lack of knowledge about the potential for stormwater quality improvements within interchanges.
Conveying project runoff/stormwaterto post-construction BMPs (PCBMPs)in these areas: It will be important to understand the hydraulics of conveying runoff to and from the infield. Elevation differences could impact how this area is or can be used for PCBMPs or stormwater management.
Regulatory acceptanceof using right-of-way areas not contiguous to the project: Interaction with regulatory agency is critical to educate them on intent, goals, objectives, and accountability for operation and maintenance. The goal should be to gain their acceptance of the concept and work with them on using these areas for stormwater management.
Loss of these areasfor pavement wasting locations for future projects: Understand the impacts on the loss of a portion of these areas for use as waste areas for road improvements.
There’s no magic bullet; the right approach will be determined by numerous groups working together with a common goal.
Next Page: Next steps
Next steps
ODOT managers must understand relevant regulatory requirements, the resources available, and the barriers. More research into runoff dynamics and capture volumes also must be conducted.
They’ll need to work with OEPA to better understand what information is needed to complete reviews and assessments as well as what FHWA may or may not allow. And they need to find additional research funds from sources such as OEPA, ODOT’s Strategic Research Plan projects, or ODOT’s Partnered Research Exploration Program.
Transportation managers are making great progress in designing high-performing green infrastructure solutions that support cleaner, healthier, more sustainable communities. It’s exciting that interstate interchanges have moved into the spotlight as an unexpected solution that can support that progress.
Mark McCabe is an associate and senior water resources professional in the Environmental Services market at Gresham, Smith and Partners (www.greshamsmith.com). His credentials include Certified Professional in Erosion and Sediment Control (CPESC), Certified Erosion, Sediment and Storm Water Inspector (CESSWI), and Certified Municipal Separate Storm Sewer System Specialist (CMS4S). E-mail mark_mccabe@gspnet.com.
