Washington State Legislature (March 12, 1919). "Chapter 92: Public Highway Appropriations". Session Laws of the State of Washington (1919 ed.). Olympia, Washington: Washington State Legislature. pp. 223–226. Retrieved February 18, 2013.
Washington State Legislature (March 19, 1923). "Chapter 185: Primary and Secondary State Highways". Session Laws of the State of Washington (1923 ed.). Olympia, Washington: Washington State Legislature. pp. 630–631. Retrieved February 18, 2013.
Staff (2011). "2011 Annual Traffic Report"(PDF). Washington State Department of Transportation. pp. 66–68. Archived from the original(PDF) on June 13, 2013. Retrieved February 18, 2013.
Washington State Legislature (March 17, 1937). "Chapter 190: Establishment of Primary State Highways". Session Laws of the State of Washington(PDF) (1937 ed.). Olympia, Washington: Washington State Legislature. pp. 939–940. Retrieved February 18, 2013.
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Staff (2011). "2011 Annual Traffic Report"(PDF). Washington State Department of Transportation. pp. 66–68. Archived from the original(PDF) on June 13, 2013. Retrieved February 18, 2013.