It runs from west to east along 172nd Street between Wenberg County Park on Lake Goodwin to a junction with SR 9 in southern Arlington, with an intermediate interchange with Interstate 5 (I-5) in Smokey Point.

At the north end of the lake, SR 531 turns east onto Lakewood Road, a rural two-lane highway that passes several suburban subdivisions.

The highway wraps around the north end of Lake Ki and Cougar Creek and turns due east onto 172nd Street Northeast at an intersection with Forty Five Road.

[4][5] The highway travels east over a set of railroad tracks into the city of Marysville, where it expands into a multi-lane road with sidewalks, bus pullouts, landscaping, a roundabout, and marked bicycle lanes.

[6] SR 531 passes several big-box retailers and apartment complexes before reaching a partial cloverleaf interchange with I-5, which marks the boundary between Marysville and Arlington.

[7][8] The overpass carrying SR 531 over I-5 is named the Oliver "Punks" Smith Bridge after a retired Arlington city councilmember who led calls for its reconstruction.

[8] The airport's main runway lies directly north of the highway, with low-flying planes making their final approach over SR 531, and the complex is ringed by a gravel multiuse trail.

After it was removed from the preliminary list of projects under the Nickel Program in January 2003, a citizens group was formed to lobby elected officials for the interchange replacement.

[19] The second phase of the project, a loop ramp channeling westbound traffic onto southbound I-5, began construction in March 2009 and was opened on August 28, 2009, six months ahead of schedule.

[11][38][39] Due to the anticipated increase in traffic caused by new industrial development in the area, a set of parallel reliever roads are also planned to be constructed in Smokey Point.