Ever wonder why is SR 531 labeled east-west?

by guest blogger Bronlea Mishler

We get a lot of questions from people who are curious about the highway system in Washington state.  I thought I'd take the time to share one of the more interesting ones we ran across lately asking why state routes are given certain numbers.

Emory of Arlington wrote to us and asked, "I was curious as to why Highway 531 is labeled an east-west route? It is my understanding that east-west routes are assigned even numbers and north-south routes are give odd numbers. Yet on either end of 531 and between each starting point there are signs posted "east" and "west" respectively?"

After doing a bit of research, we discovered that Emory is correct that SR 531 is, indeed, an east-west highway, even though it has been assigned an “odd” number. It got the unusual designation on April 1, 1992 (seriously), when we took over the highway from Snohomish County.

If you keep track of the state highways in Snohomish County, you’ll know that the numbering scheme doesn’t leave much room for flexibility. State Routes 526 and 527 meet up with I-5 in the Everett area, and SR 528 and SR 529 meet up with I-5 in Marysville. SR 530 crosses I-5 in the Arlington area, and SR 532 ends at I-5 in Stanwood. When we added this “new” state route in 1992, we only had one numbering option left: SR 531. Even though the highway is south of SR 530 and SR 532, and even though it runs east-west, the only number we could give it was an odd one.

You can read more about how we number highways and interstates.