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Transportation planning for unincorporated King County - King County, Washington
Traffic on 140th Avenue SE and SE Petrovitsky Road in unincorporated King County.
Transportation needs are growing in unincorporated King County. To help manage this growth, the King County Comprehensive Plan serves as a 20-year guide for development in these areas.
The Road Services Division leads the transportation chapter of the plan.
We use several planning tools to make sure our roads, bridges and other infrastructure meet the needs of everyone who lives, works and travels in Unincorporated King County, including:
- Transportation Needs Report – Identifies long-term improvements to help people get around safely and efficiently.
- Transportation Concurrency Program – Helps coordinate land development with transportation upgrades early in the planning process, so communities grow in a smarter, more efficient way.
Transportation Needs Report and the Transportation Concurrency Program
Transportation Needs Report (TNR)
The Transportation Needs Report is a long-term list of transportation improvement needs in unincorporated King County. It is a component of the King County Comprehensive Plan and fulfills state requirements as specified in the Washington State Growth Management Act.
Current status
The latest version of the TNR was adopted by the King County Council on December 10, 2024, as part of the 2024 King County Comprehensive Plan update. The following is the final adopted version of the 2024 TNR:
NOTE: if you are using Internet Explorer, you may need to download the PDF file below to view it properly (right-click the file name and select "save target as" to save the file to your computer).
Differences between the Transportation Needs Report and Capital Improvement Program
The Capital Improvement Plan (CIP) is updated annually and partially funds projects for the next six years. In contrast, the Transportation Needs Report (TNR) focuses on long-term goals set by the Comprehensive Plan but currently lacks funding for most projects.
For the current list of funded transportation projects, please refer to the Road Services Division CIP program.
Transportation Concurrency Program
Transportation concurrency is another tool the County uses to ensure roads can keep up with new growth. It supports the Growth Management Act, a law which says local governments must make sure that public facilities and services can keep up with new development.
In King County, the Transportation Concurrency Program is how the County follows this law. It checks whether roads in different areas can handle more traffic from new homes or businesses.
How concurrency works in King County
The County divides areas into travel sheds. These are groups of roads where people drive in similar patterns, kind of like neighborhoods that share the same main roads.
Each travel shed is tested to see how well traffic is flowing on the main roads, called arterial roads.
- If 15 percent or less of the roads are too crowded or slow, the area passes the test.
- If more than 15 percent of the roads are too crowded or slow, the area fails the test, and new development may be limited until improvements are made.
Travel shed status is shown on the concurrency map. The map is reviewed and updated every two years or when directed by the King County Council.
Current status
The latest Transportation Concurrency Update Report was completed and sent to the King County Council in July 2024.
Here’s what the report shows:
- All travel sheds received a ‘pass’ rating.
- There were no changes in pass/fail status since the last update in 2022.
- The report includes information about findings, methods used and updated maps.
View the 2024 Transportation Concurrency Update Report (600KB)
If you are looking for the current rules and standards King County uses for concurrency, you can find them in the King County Code Title 14. Chapter 14.70
Frequently asked questions
- How can I check my property's concurrency status?
Check your property's transportation concurrency status using the King County Parcel Viewer. Input your property's address or 10-digit parcel identifier. After the application shows your property information, select "Districts Report" located on the lower left-hand side of the page. On the "Districts Report" refer to the row titled "Transportation Concurrency Management" for your "Pass" or "Fail" determination. Technicians at the Department of Permitting and Environmental Review (DPER) handling your application will check this on your pre-application form. - What do I do if my property fails concurrency?
Should your property be identified as failing concurrency, check with a DPER staff member to see if your property or development proposal qualifies under the category “Minor Developments and Public and Educational Facilities,” which may allow you to proceed with your application (see King County Code 14.70.285). If the proposal does not meet these criteria, you cannot proceed with your development proposal until the property is identified as passing concurrency.
Arterial Classification System
Arterial functional classification is the organization of a road system into groups according to the “function” each road serves or is intended to serve. The main functions for any road are 1) to provide mobility for users and, 2) to provide access to adjacent land uses. The degree to which the road serves movement of traffic or access to adjacent land uses is the basis for its functional classification.
Arterial functional classification is used in transportation planning, roadway design and allocation of road improvement funds. In unincorporated King County, there are three types of arterial roadways:
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Principal arterials—Provide for movement across and between large subareas of an urban region and serves predominantly "through traffic" with minimum direct service to abutting land uses.
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Minor arterials—Provide for movement within the larger subareas bound by principal arterials. A minor arterial may also serve "through traffic" but provides more direct access to abutting land uses than does a principal arterial.
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Collector arterials—Provide for movement within smaller areas which are often definable neighborhoods, and which may be bound by arterials with higher classifications. Collectors serve very little "through traffic" and serve a high proportion of local traffic requiring direct access to abutting properties. Collector arterials provide the link between local neighborhood streets (i.e. non-arterials) and larger arterials.
The majority of the roads in the King County road system are not designated as arterials and function as local neighborhood streets.
The Arterial Functional Classification Map (335KB) is a component of the King County Comprehensive Plan (Appendix C – Transportation) and is reviewed periodically for system changes. Changes to the arterial classification are handled through the Comprehensive Plan review and adoption process. The Comprehensive Plan is normally reviewed annually, with a major update scheduled every ten years, and a midpoint limited update every five years. Citizens can request changes to the Comprehensive Plan through the formal "Comprehensive Plan Amendment Docketing process".