State Route 507 begins at a diamond interchange with , co-signed as in Centralia. Traveling east as Mellen, Alder and West Cherry Streets, the highway crosses railroad tracks owned by BNSF Railway and used by Amtrak's Cascades and Coast Starlight routes, both of which serve the Centralia Amtrak station. The roadway later intersects Pearl Street, the only couplet on SR 507, which parallels Tower Avenue through Downtown Centralia. The street then becomes Tower Avenue and turns north to pass the Centralia Amtrak station. SR 507 realigns west as Sixth Street to intersect and become Pearl Street, once again traveling northeast as Downing Road to leave Centralia. Still parallel to BNSF Railway tracks, the road leaves Lewis County, enters Thurston County, passes Bucoda and turns north to intersect an old segment of in Tenino. Within Tenino, the highway stops paralleling the BNSF tracks and goes east through the city as Sussex Avenue and starts to parallel a route of the Tacoma Rail eastward out of the city. Passing through Rainier as Binghampton Street, the roadway intersects the eastern terminus of in Yelm and then turns southeast as Yelm Avenue, before leaving both Yelm and Thurston County to enter Pierce County on a bridge over the Nisqually River. Once in Pierce County, SR 507 intersects in McKenna and continues north as the Spanaway McKenna Highway to Roy, where the highway turns east and then northeast into Fort Lewis. Immediately after leaving Fort Lewis, the roadway ends at an intersection with in Spanaway. Between SR 510 in Yelm and SR 702 in McKenna, the roadway had an estimated daily average of 19,000 motorists in 2007, causing the segment to be the busiest on SR 507. The busiest segment in 1970 was the Maple Street junction in Downtown Centralia, with an estimated daily average of 14,000 motorists. SR 507 is also the southern segment of the East Pacific Highway, which runs from Centralia to Sumas.
Couplet
Within Downtown Centralia, SR 507 splits into two streets, northbound on Tower Avenue and southbound on Pearl Street, which has been designated SR 507 CO Pearl. The busiest segment of the long couplet was the Cherry Street intersection, with an estimated daily average of 9,700 motorists in 2007.
History
The first appearance of a highway located on the current route of SR 507 was in a 1916 map of the Chehalis area. A road extending northwest from Centralia to Roy was shown serving the communities that SR 507 currently serves. In 1937, during the creation of the Primary and secondary highways, was established, running from Tenino to Spanaway. A section of 507 houses the Tenino Downtown Historic District. In 1943,, running from Centralia to Tenino, was created. In 1964, a highway renumbering replaced both SSH 5H and SSH 1N with SR 507. A left turn lane was installed at the Yew Street intersection east of the and interchange in Centralia on May 24, 2007., when completed, is predicted to reduce congestion on SR 507. A section of the highway near Rainier was renamed the Sgt. Justin. D. Norton Memorial Highway in 2017 to honor a local soldier.
