Since the 1964 state highway renumbering, which established the current state route system, the Washington State Department of Transportation has decommissioned thirty state routes. Once a highway has been decommissioned, the highway is turned over to the local county or city that it resided in, who is then responsible for all maintenance on the former highway. All former highways are codified in Washington law under the Revised Code of Washington, chapter 47.17, section 420.
SR 126 was a state route in the U.S. state of Washington. It was an auxiliary route of US 12. It started at US 12 (at Dayton), then headed east to US 12 again (near Pomeroy), where it ended. In January 1964, SSH 3L became SR 126. SR 126 was dropped out of the system in 1992 because it was mostly very steep and unpaved. The approximate route follows Patit Road, Hartstock Grade Road, Tucannon Road, Blind Grade Road, Linville Gulch Road, and Tatman Mountain Road.
SR 901 was created in 1964 from Secondary State Highway 2D. At the time of its creation, SR 901 began at the intersection of Lake Washington Boulevard and State Route 520, on the border of Kirkland and Bellevue. It then traveled north along Lake Washington Blvd. to downtown Kirkland. At the intersection of Lake St. and Central Way, SR 901 turned right, traveling east along Central Way. It then continued as Redmond Way into Redmond turning south onto West Lake Sammamish Parkway when the roads intersected. It then followed West Lake Sammamish Parkway into Issaquah, ending at its intersection with State Route 900. SR 901 also had a spur leading from West Lake Sammamish Parkway into downtown Redmond along Redmond Way.
In 1971, SR 901 was broken into two parts. The western part, from SR 520 to the intersection of Redmond Way and West Lake Sammamish Parkway (including the spur into Redmond), was renamed State Route 908. The remainder retained the SR 901 designation, with one exception; West Lake Sammamish Parkway lost its state route designation from Exit 13 of Interstate 90 to its intersection with SR 900.
In 1992, SR 901's path was changed again; now it ran through the city of Sammamish along East Lake Sammamish Parkway from Front Street in Issaquah to State Route 202 east of downtown Redmond. Shortly thereafter, SR 901 was completely dropped as a state route in Washington.