Washington State's highways are designated by the Legislature and codified in Chapter 47.17 RCW. State Route 501 (SR 501) is a 14-mile route in Clark County located in southwest Washington. SR 501 is split into two sections; a three-mile northern section running east-west through the City of Ridgefield from Pioneer Street to Interstate-5 (I-5) and an 11-mile southern section beginning at the interchange of I-5 near downtown Vancouver and ending south of Post Office Lake in the Ridgefield National Wildlife Refuge. The southern section is designated as the Erwin O. Rieger Memorial Highway.
The thee-mile section of SR 501 between mile posts 16.91 to 19.88 is transferred to the City of Ridgefield, removing it from the state highway system. The 11-mile southern section of SR 501, known as the Erwin O Rieger Memorial Highway remains in the state highway system.