Transportation planning

Transportation Concurrency Program

Current status

The 2020 Transportation Concurrency Update Report was completed and transmitted to the King County Council on September 29, 2020. No changes occurred in travel shed pass/fail status since the previous update in 2018. As a result, the 2018 travel shed boundary map and test results map remain in effect. The 2020 Transportation Concurrency Update Report includes update methodology, findings, and both maps.

The current adopted Concurrency regulations and level of service standards can be found in Title 14, Chapter 14.70 of the King County Code.

About transportation concurrency

Concurrency is a land use regulatory framework under the Washington State Growth Management Act (GMA), passed in 1990. It is used by local governments to ensure that sufficient public facilities are in place for any new land use development. It also supports the overarching goals of the GMA: Focusing growth in urban communities, reduction of sprawl, and protection of natural and agricultural resource lands.

King County first implemented the Transportation Concurrency Management program by adopting its first Comprehensive Plan following the GMA in 1994, with the program becoming effective in 1995. Transportation concurrency policies can be found in Chapter 8 ("Transportation") of the current adopted King County Comprehensive Plan.

Key elements of the program are summarized as follows:

• Travel time data is collected by corridor segments on County principal and minor arterials
• Concurrency testing is by geographic “travel sheds” where travel patterns share common characteristics
• Concurrency testing evaluates travel time by roadway mileage within each travel shed
• The concurrency map is reviewed and updated every two years or when directed by the King County Council
• Rural Mobility Areas are designated rural areas (the towns of Vashon, Snoqualmie Pass and Fall City) that support a greater variety of transportation mode choices than typically found in most rural areas. These areas have level of service standards which support and encourage people to use alternative modes of transportation
• 85 percent of travel shed arterial mileage must meet concurrency standards for the travel shed to pass the concurrency test
• Residential and nonresidential proposals are tested by the same concurrency map
• Concurrency is based on pass or fail of travel shed status as shown on the concurrency map
• Clear identification is made of failing corridor routes that are the primary reason a travel shed is out of compliance

Frequently-asked questions

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:

• 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.

• 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.

• 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 PDF 335KB is a component of the King County Comprehensive Plan (Technical 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 eight years, and a midpoint limited update every four years. Citizens can request changes to the Comprehensive Plan through the formal "Comprehensive Plan Amendment Docketing process".