During the creation of the primary and secondary state highways in 1937, State Road 15 was added back to the state highway system as part of SSH 1S, which traveled from Primary State Highway 1 (PSH 1) and U.S. Route 99 (US 99) to SSH 1U in Battle Ground and turned west to end at PSH 1 and US 99 north of Mount Vista. PSH 1U, also established in 1937, traveled south from SSH 1S in Battle Ground to SSH 8A in Orchards. The Yale Bridge was maintained by Clark and Cowlitz counties until the 1940s and had its timber approach spans replaced with steel in 1958 under maintenance of the Department of Highways.