State Route 501-Erwin O. Rieger Memorial Highway

In 1964, SR 501 started at Jct I-5 in Vancouver and headed west via the port area to the west side of Vancouver Lake. 1963 legislation had designated a route continuing north to Ridgefield that as of 2001 has not yet been completed. A temporary route extending north from the Vancouver Lake area to the south end of the Ridgefield National Wildlife refuge uses what had been built as a county road. There is a missing gap in SR 501 between the south end of the wildlife refuge and Ridgefield. In downtown Ridgefield, SR 501 begins again and heads east to I-5, where SR 501 ends

Part of the ultimate alignment of SR 501 near Vancouver Lake was built and has been designated as the Erwin O. Rieger Memorial Highway. This section of SR 501 is not posted as a state highway. In 2000, Vancouver completed a western extension of Mill Plain Blvd from downtown to the port area. In March 2001, SR 501 was rerouted from I-5 to the port area via Mill Plain Blvd. The route of SR 500 that was opened to traffic and signed as thus as of January 2001 was 15.18 miles long.

The 2024 session of the Washington State Legislature removed the portion of SR 501 from downtown Ridgefield to I-5 from the state highway system. This portion is what is known in the city as Pioneer St. The legislation making the change is House Bill 2318.

Before 1964, SR 501 had been SSH 1T.