State Route 538 (SR 538) begins at the (I-5) interchange in northern Mount Vernon located south of the Skagit River. The roadway, which handled a daily average of 27,000 motorists at the interchange in 2008, is named College Way and travels east through a commercial zone, passing Riverside Drive, the former route of (US 99), and crossing a set of rail tracks used by BNSF Railway. Transitioning from a commercial to residential area, the Mount Vernon campus of the Skagit Valley College, located on the north side of the highway, is passed and eventually SR 538 leaves Mount Vernon city limits. The road turns southeast and ends at a roundabout with within Mount Vernon's urban growth boundary.
