King County Road Services - Frequently-asked questions

Arterials are eligible for state and federal funds for improvements such as curbs, gutters and sidewalks. Most of the county’s Capital Improvement Program (CIP) funds are oriented to the arterial system. Arterials are first to be plowed during snowstorms, first to be kept open in emergencies, are maintained to a higher standard, and are eligible for amenities such as walkways, pathways and equestrian trails. Non-arterial streets generally lack lane markings like outside edge lines or a centerline. Learn more about arterial classification.

Arterial streets generally have higher traffic volume. Traffic calming measures such as speed humps are usually not appropriate for arterial streets because they are used by emergency vehicles. Commercial traffic, such as trucks, should use arterial rather than local roads. Learn more about arterial classification.

Not necessarily. The designation means that it is one of the more important roads in the roadway system. The arterial designation itself will not lead to more traffic. Through traffic operations, the County usually directs traffic away from neighborhood streets onto streets that are better designed to handle more traffic, such as arterials. Learn more about arterial classification.

The term “arterial” does not refer to any busy street or road. It is an official designation conferred by the County Council. Learn more about arterial classification.

The arterial functional classification is included in the transportation portion of the King County Comprehensive Plan (Technical Appendix C – Transportation). As a part of the Comprehensive Plan, the arterial system can be reviewed annually and changed, if appropriate, when the Comprehensive Plan is amended. To suggest changes to the Comprehensive Plan, please follow these docketing procedures.

King County does not recommend speed humps on arterial roadways. Arterials are considered the primary routes between communities, with speeds ranging from 35 mph to 55 mph and traffic volumes over 2,000 vehicles per day. These routes are designated to carry traffic from one neighborhood or city to another and are also the critical lifeline roadways used for fire and emergency response vehicles. The arterial roadway design is characterized by features that enhance traffic flow and increase safety, which include adding separated pedestrian facilities and illumination while minimizing direct residential/commercial access, on-street parking, and narrow, curvy lanes. Speed humps are a traffic calming treatment typically used to prevent traffic from using residential streets as a cut-through to access the arterial roadway system. If speeding is a problem, Traffic Maintenance and Engineering can determine the extent of the problem and develop an appropriate solution.