Introduction to Washington Expressways:
Washington builds a large number of expressways, both as 4-lane divided highways and “super-2” expressways with only two lanes. An at-grade expressway is a highway with partial control of access. Expressways are different from standard roads because they have severe restrictions placed on the frequency of intersections and private driveways allowed. No commercial driveways are allowed on expressways. Each expressway must meet the following standards for access:
At an at-grade intersection on a partial control limited access highway, control will be established and acquired along the crossroad for a minimum distance of 300 ft from the center line of the highway. If another frontage or local road is located at or within 350 ft of the at-grade intersection, limited access will be established and then acquired along the crossroad for the required minimum 300 ft and for an additional minimum distance of 130 ft in all directions from the center line of the intersection of the frontage or local road or the ends of the raised splitter islands of a roundabout and the crossroad. On multilane highways, measurements will be made from the center line of the nearest directional roadway. An approved access deviation is required if the limited access control falls short of 300 ft and for any access that has been allowed to remain within the first 130 ft. At-grade intersections with public roads are limited to the number allowed for the functional classification of highway involved as follows:
Principal Arterial - If the ADT is less than 2,000, one mile spacing (minimum), center line to center line. If over 2,000 ADT within 20 years, plan for grade separation.
Minor Arterial - If the ADT is less than 2,000, one-half mile spacing (minimum), center line to center line. If over 2,000 ADT within 20 years, plan for grade separation.
Collector - Road (or street) plus property approaches not more than six per side per mile. However, with approval from the State Design Engineer, shorter intervals may be used where topography or other conditions restrict the design. When intersecting roads are spaced farther apart than one per mile, median crossings may be considered for U-turns in accordance with Chapter 910. Keep U-turns to a minimum, consistent with requirements for operation and maintenance of the highway.
To discourage movement in the wrong direction on multilane highways, locate private approaches 300 ft or more from an at-grade intersection. At a tee intersection, a private approach may be located directly opposite the intersection or a minimum of 300 ft away from the intersection. Ensure that a private approach directly opposite a tee intersection cannot be mistaken for a continuation or part of the public traveled way.
(B) Access Approaches
Partial control is exercised to the level that, in addition to intersections with selected public roads, some crossings and private driveways may be allowed.
(1) Approach Types. Partial control limited access highways allow at-grade intersections with selected public roads and selected residential and farm approaches. Commercial approaches are not allowed direct access to partial control limited access highways. Commercial access is allowed only by way of public roads. The type of approach provided for each parcel takes into consideration present and potential land use and is based on an economic evaluation.
(2) Design Considerations. The following considerations are used to determine the number and location of access approaches on partial control limited access highways.
1. Access approaches must be held to a minimum. The number is limited as follows:
• Principal arterial - 2 per side per mile.
• Minor arterial - 4 per side per mile.
• Collector - 6 per side per mile including at-grade intersections
2. Approaches in excess of the number listed in 1., above, may be allowed as stage construction if approved by the State Design Engineer.
3. Approaches are not allowed for parcels that have reasonable access to other public roads unless the parcel has extensive highway frontage.
4. Relocate or close approaches located in areas where sight limitations create undue hazard.
5. Allow only one approach for each parcel except for very large ownerships, or where terrain features do not allow the property to be served by a single approach. This includes contiguous parcels under a single ownership.
6. Where possible, locate a single approach to serve two or more parcels.
7. The approved design is to provide for future development of frontage roads that will eliminate an excessive number of approaches.
Washington pages by Chris Kalina. Additional thanks to Mark Bozanich, Stephen Dailey. Design standards are from the WSDOT Design Manual.
Last Updated: 12/9/04
Please send any comments, suggestions, corrections, additional information or pictures about this page to: