The present route of US 2 follows several wagon roads that were built in the late 19th century by local railroad companies, including the Stevens Pass Highway along the Skykomish River. The state of Washington began maintaining sections of what would become US 2 with the extension of State Road 7 in 1909, from Pashastin to Spokane on the Sunset Highway and later State Road 2. In addition to State Road 2, State Road 23 was created in 1915, traveling north from Spokane to Newport, and was renumbered to State Road 6 in 1923. The Stevens Pass Highway was transferred to state maintenance in 1931 with the establishment of State Road 15, traveling from Everett to Peshastin. The United States Highway System was adopted on November 11, 1926, and designated US 10 on the future route of US 2 from Peshastin to Spokane and US 195 from Spokane to Newport. US 10 was re-routed in 1939 and replaced by US 10 Alternate, which was routed across Stevens Pass in the 1940s and itself replaced by US 2 in 1946. The primary state highways were replaced by the current state route system during the 1964 state highway renumbering, and US 2 replaced its three concurrent routes. US 2 underwent conversions to limited-access highways during the next several decades, including the completion of the Hewitt Avenue Trestle and a bypass of Snohomish. A series of projects is planned to improve the US 2 corridor between Snohomish and Skykomish by expanding the highway near various cities and the completion of a bypass around Monroe.