Interstate 605 (Washington)

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Interstate 605

Proposed 1998 corridor of I-605 highlighted in red
Route information
Auxiliary route of I-5
Defined by RCW 47.17.%section%
StatusNever built
NHSEntire route
CountryUnited States
Highway system
SR 603 SR 702

Interstate 605 (I-605) is the popular moniker given to several proposals for a new auxiliary Interstate Highway bypassing I-5 and I-405 in the U.S. state of Washington. Proposals have been heard from since the 1960s, including highways connecting from I-5 all the way to the Canada–US border, and some just between I-5 and I-90. The Washington State Department of Transportation (WSDOT) has no projects designated I-605 at this time. However, some I-605 proposals have included State Route 18, which has been partially constructed as a freeway.


Some of the first plans for a new Interstate Highway freeway, bypassing I-405, surfaced in 1965 while the highway was still under construction.[1] The first proposal was to create a new highway between I-405 and the west banks of Lake Sammamish. Residents however forced the highway to the east banks of the lake after voicing their concerns. Residents on the east side of the lake voiced similar concerns and the plan was later dropped.[2] While the moniker of "I-605" was applied to the proposal, in official studies it was only referred to as the Auburn–Bothell Highway or by the provisional designation of Primary State Highway 19 (PSH 19).[3][4]

In 1998, the Washington State Legislature ordered a $500,000 study to investigate the benefits of extending SR 18 north to Everett through the Snoqualmie Valley.[5][6] The plan was dropped as the study found that on average only five minutes would be saved over current routes.[2] In 2002, Bellevue Square owner Kemper Freeman, Jr. made his support known for a new freeway linking Snohomish County via the Snoqualmie Valley.[7]

Another $500,000 study was ordered in 2003 by the legislature, creating a new commerce corridor to link Lewis County in the south to the Canada–US border in the north.[2] However the study showed that a highway existing north of I-90 was not economically feasible. The study proposed a toll road only for trucks, since the presence of passenger cars would discourage truck drivers from using the new alternate route. The highway was estimated to cost between $13.5 and $19 billion.[8]

Related projects

The state currently has no plans to build I-605. However, the SR 18 corridor is part of most I-605 proposals. WSDOT has widened most of SR 18 between I-5 and Hobart to full freeway standards, while the remainder is a two-lane mountainous highway with truck lanes on uphill segments. WSDOT once proposed to creating a full limited-access freeway for the remainder,[9] but updated preliminary plans would upgrade it to a four-lane divided highway, with right-in/right-out at Tiger Mountain and a diverging diamond interchange at I-90.[10][11] While SR 18 has been a part of most I-605 proposals, it only bypasses the Greater Seattle area on the southern and eastern sides.[12]

See also


  1. ^ Barr, Robert A. (December 1, 1965). "Beginning Urged Now on East Side's Traffic Problem". The Seattle Times. p. 7.
  2. ^ a b c Singer, Natalie (July 15, 2004). "State study revives idea of new Western Washington highway". The Seattle Times. The Seattle Times Company. Archived from the original on December 23, 2017. Retrieved November 6, 2010.
  3. ^ "Auburn–Bothell Highway Study Phase 1 – Study Design". Washington State Legislature Joint Committee on Highways. February 1970. p. II-1. Retrieved October 6, 2021 – via WSDOT Library Digital Collections.
  4. ^ Andrews, G. H. (January 8, 1971). "A Legislative Study: Kenmore to Swamp Creek". Washington State Legislature Joint Committee on Highways. p. 2. Retrieved October 6, 2021 – via WSDOT Library Digital Collections.
  5. ^ Herrinton, Gregg (April 28, 1998). "Interstate 605 could help ease traffic mess". The Columbian. p. B2. Retrieved February 18, 2023 – via
  6. ^ Whitely, Peyton (April 24, 1998). "Is Freeway the Way? Proposed new north–south interstate on Eastside has some mountains to climb". The Seattle Times. p. B1. Retrieved December 30, 2016.
  7. ^ Gilmore, Susan (August 24, 2003). "Some freeway plans never went anywhere". The Seattle Times. The Seattle Times Company. Retrieved November 6, 2010.
  8. ^ "Valley will not see proposed foothills highway". Snoqualmie Valley Record. Sound Publishing Inc. October 28, 2004. Retrieved November 6, 2010.
  9. ^ Mishler, Bronlea. "Project — SR 18 - Issaquah Hobart Road to I-90". Washington State Department of Transportation. Archived from the original on November 21, 2010. Retrieved November 7, 2010.
  10. ^ Kunkler, Aaron (August 3, 2020). "State route 18 interchange project still scheduled to break ground next year". Snoqualmie Valley Record. Retrieved February 16, 2021.
  11. ^ "SR 18 — Issaquah/Hobart Rd to Raging River — Widening — Project design". Washington State Department of Transportation. Retrieved February 12, 2021.
  12. ^ Washington State Highways, 2014–2015 (PDF) (Map). Washington State Department of Transportation. 2014. Puget Sound inset. Archived from the original (PDF) on February 21, 2017. Retrieved February 16, 2021. {{cite map}}: External link in |inset= (help)

Further reading

External links