A suggestion for refinement with an ulterior motive (i.e. I want a fraction of a mile):

WA 20 has a point at I-5, a point at the intersection of Burlington Boulevard and Avon Avenue, then nothing until WA 9. I think a point should be added at the intersection of Burlington Boulevard and Rio Vista Avenue - this would create a straight segment along Burlington that would aid anyone traveling Old US 99 - and a point added at the east intersection with Cascade Highway, to better align the diagonal that goes northeastward to WA 9.

And while I'm here, could I get a point on WA 523 at 15th Avenue, or is that too close to I-5?