Arterial Classification System for Unincorporated King County

• Map of unincorporated King County arterials — Adopted Sept.18, 2006
  (2MB .pdf )
• Frequently-asked questions
• 2007 King County Road Standards

What is arterial functional classification?

Arterial functional classification is the division of a road system into a number of categories or groups according to the “function” each road serves or is intended to serve. The main functions for any road are 1) to provide mobility, or the movement of traffic 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, in roadway design and for the allocation of road improvement funds. In unincorporated King County, there are three types of arterial roadways:

• Principal arterial—Provides for movement across and between large subareas of an urban region and serves predominantly "through traffic" with minimum direct service to abutting land uses. This category includes freeways and major highways under the jurisdiction of the Washington State Department of Transportation.
• Minor arterial—Provides 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.
• Collector arterial—Provides 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.
• Local roads—The majority of King County’s roads are local roads and not designated as arterials. These roads provide access to land uses and connections to the arterial system.

The arterial map is a component of the King County Comprehensive Plan (Technical Appendix C – Transportation), and is reviewed periodically for arterial 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 each four years. Citizens can request changes to the Comprehensive Plan through the formal “Comprehensive Plan Amendment Docketing process”. Arterial changes were last made with the adoption of the 2006 Update to the King County Comprehensive Plan, Ordinance 15028, on Sept. 18, 2006.

For further information, please contact:

David Gualtieri
Transportation Planner
Road Services Division
King County Department of Transportation
201 South Jackson Street
MS KSC-TR-0317
Seattle WA 98104-3856
Telephone: 206-263-4704
FAX: 206-296-0566

Updated: Sept. 19, 2007