Washington State Route 501

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State Route 501, also known as the Erwin O. Rieger Memorial Highway, is a 13.97-mile state highway in Clark County, Washington. It has two separate pieces: a north–south section from I-5 in Vancouver to the Ridgefield National Wildlife Refuge, and a west–east section from Ridgefield to I-5.

History in brief
- The route began as Secondary State Highway 1T (SSH 1T) in 1937.
- It was renumbered to SR 501 in 1964.
- It was named the Erwin O. Rieger Memorial Highway in 1991.
- In 2024, the northern section was transferred to the City of Ridgefield.

Southern section (11.00 miles)
- Starts at Mill Plain Boulevard with I-5 in downtown Vancouver, travels west, and splits into a one-way pair on Mill Plain Boulevard and 15th Street before rejoining.
- Crosses a BNSF rail yard, enters the Port of Vancouver, then becomes Lower River Road and narrows to two lanes by Vancouver Lake.
- Follows the Columbia and Lake rivers north past the Shillapoo Wildlife Recreation Area, ending south of Post Office Lake in the Ridgefield National Wildlife Refuge.
- Mill Plain Boulevard was extended west to serve the Port of Vancouver, a project completed in 2000.
- A segment south of the Columbia River reclamation was closed in 2015 and transferred to Clark County in 2016; that portion was vacated to surrounding property owners.

Northern section (2.97 miles)
- Begins as Pioneer Street at Main Avenue near Ridgefield City Hall and runs east through downtown Ridgefield, past View Ridge Middle School.
- Passes Gee Creek, then goes through two roundabouts at 45th Avenue and 56th Place before ending at I-5.

Traffic and significance
- WSDOT data (2011) show the busiest SR 501 section overall was west of I-5 at C Street (about 13,000 vehicles per day); the least busy was south of Shillapoo Wildlife Recreation Area (about 650).
- The northern section’s busiest point was the I-5 interchange (about 11,000); the least busy was Main Street in Ridgefield (about 3,200).
- The segment between I-5 and the Port of Vancouver is part of the Highway of Statewide Significance.

Jurisdiction and location
- The entire highway is in Clark County, Washington, though the northern section is now under the City of Ridgefield’s jurisdiction (as of 2024).