In 1923, the state highway system was restructured completely, incorporating numbers instead of names. The Olympic Highway became State Road 9, the Pacific Highway became State Road 1, the National Park Highway absorbed the Naches Pass Highway and remained State Road 5, and the Inland Empire Highway became State Road 3, but its branch from Dayton to Clarkston remained a branch of the now non-existent Inland Empire Highway. A system of national highways that improved on the concept of auto trails was formed in late 1925. The final plan for the system—which became the U.S. routes—was approved on November 11, 1926. One of the routes included in the plan was US 410, which extended from US 101 in Aberdeen to US 95 in Lewiston, Idaho. Parts of US 410 were concurrent with other new highways, including US 99 from Olympia to Tacoma and US 97 in Yakima. In 1937, the state highway system changed to a primary and secondary system. US 410 remained the same, but its concurrent state highways had their designations changed by the state. State Road 9 became Primary State Highway 9 (PSH 9), State Road 1 and US 99 became PSH 1, State Road 5 became PSH 5, State Road 3 became PSH 3, and the Inland Empire Highway branch from Dayton to Clarkston became a branch of PSH 3.