Washington State Legislature (March 4, 1909). "Chapter 51: Providing for the Survey of Certain State Roads". Session Laws of the State of Washington (1909 ed.). Olympia, Washington: Washington State Legislature. p. 95. Retrieved April 3, 2013.
Washington State Legislature (March 12, 1913). "Chapter 65: Classifying Public Highways". Session Laws of the State of Washington (1913 ed.). Olympia, Washington: Washington State Legislature. p. 221. Retrieved April 3, 2013.
Washington State Legislature (March 19, 1915). "Chapter 164: Classification of Public Highways". Session Laws of the State of Washington (1915 ed.). Olympia, Washington: Washington State Legislature. p. 486. Retrieved April 3, 2013.
Washington State Legislature (March 10, 1917). "Chapter 75: Appropriation for Primary and Secondary Highways". Session Laws of the State of Washington (1917 ed.). Olympia, Washington: Washington State Legislature. p. 257. Retrieved April 3, 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. 628–629. Retrieved April 3, 2013.
Washington State Legislature (March 17, 1937). "Chapter 190: Establishment of Primary State Highways". Session Laws of the State of Washington (1937 ed.). Olympia, Washington: Washington State Legislature. pp. 934, 937, 940–941. Retrieved April 3, 2013.
"Chapter 1: Introduction"(PDF). US 2 Route Development Plan. Washington State Department of Transportation. November 2007. Retrieved April 3, 2013.
Prahl, C. G. (December 1, 1965). "Identification of State Highways"(PDF). Washington State Highway Commission, Department of Highways. Archived from the original(PDF) on February 17, 2017. Retrieved June 9, 2009.
"Segment 1: Snohomish to west Monroe"(PDF). US 2 Route Development Plan. Washington State Department of Transportation. November 2007. Retrieved April 3, 2013.
Prahl, C. G. (December 1, 1965). "Identification of State Highways"(PDF). Washington State Highway Commission, Department of Highways. Archived from the original(PDF) on February 17, 2017. Retrieved June 9, 2009.