A 1900 map of the Tacoma area showed a roadway extending north from Spanaway to Tacoma that would later become SR 7. In 1909, the Alder-Kosmos Road, numbered State Road 18, was added to the state highway system and ran from Kosmos north through Morton and Elbe to Alder. The National Park Highway was created in 1913 and extended from the Pacific Ocean to Tacoma and south to Elbe, where it turned east into Mount Rainier National Park. Both highways were replaced by two branches of State Road 5 in 1923, which traveled from Tacoma to Mount Rainier and Elbe to Chehalis. State Road 5 became Primary State Highway 5 (PSH 5) during the creation of the Primary state highways in 1937 and the Tacoma-Mount Rainier branch remained the same, but the Elbe-Chehalis branch was shortened to Kosmos.