Interstate 5 in Washington (I-5) is a 276.62-mile (445.18 km) highway in the U.S. state of Washington that extends from its border with Oregon to its border with Canada. Serving the cities of Vancouver, Kelso, Chehalis, Centralia, Olympia, Tacoma, Seattle, Everett, Mount Vernon, and Bellingham, it is the main route between Portland, Oregon, and Vancouver, British Columbia.It is the only interstate to traverse the whole north–south length of Washington, but the undivided highways U.S.