Interstate 405 (Washington)

Interstate 405
Interstate 405
	I-405 highlighted in red
Route information
	Auxiliary route of I-5
	Maintained by WSDOT
Length	30.30 mi (48.76 km)
Existed	1957–present
NHS	Entire route
Major junctions
South end	I-5 / SR 518 in Tukwila
	SR 167 in Renton; I-90 in Bellevue; SR 520 in Bellevue; SR 522 in Bothell;
North end	I-5 / SR 525 in Lynnwood
Location
Country	United States
State	Washington
Counties	King, Snohomish
Highway system
	Interstate Highway System; Main; Auxiliary; Suffixed; Business; Future; State highways in Washington; Interstate; US; State; Scenic; Pre-1964; 1964 renumbering; Former;

Interstate 405 (I-405) is a north–south auxiliary Interstate Highway serving the Seattle region of Washington, United States. It bypasses Seattle east of Lake Washington, traveling through the Eastside area of King and Snohomish counties, providing an alternate route to I-5. The 30-mile (48 km) freeway serves the cities of Renton, Bellevue, Kirkland, and Bothell. I-405 terminates at I-5 in Tukwila and Lynnwood, and also intersects several major highways, including SR 167, I-90, SR 520, and SR 522.

The Eastside highway was originally built in the early 20th century to connect cities along the lake and was formally added to the state highway system in 1937 as Secondary State Highway 2A (SSH 2A). A freeway replacement for SSH 2A was proposed in the 1940s by the state government and designated as I-405 as part of the federal Interstate Highway program, with the first section beginning construction in 1956 and completed in 1965. It was initially signed as SR 405 until the freeway was fully completed in 1971; since then, the highway has been expanded to add lanes for high-occupancy vehicles and toll users. I-405 is one of the most congested highways in the Seattle area and is known for its meandering "S-curves" through Renton, which were straightened in the 1990s.

^ Multimodal Planning Division (February 4, 2020). State Highway Log Planning Report 2019, SR 2 to SR 971 (PDF) (Report). Washington State Department of Transportation. pp. 1363–1380. Retrieved July 27, 2020.
^ "Table 2: Auxiliary Routes of the Dwight D. Eisenhower National System Of Interstate and Defense Highways". Federal Highway Administration. December 31, 2016. Retrieved December 22, 2017.

[log-1] Multimodal Planning Division (February 4, 2020). State Highway Log Planning Report 2019, SR 2 to SR 971 (PDF) (Report). Washington State Department of Transportation. pp. 1363–1380. Retrieved July 27, 2020.

[FHWA-log-2] "Table 2: Auxiliary Routes of the Dwight D. Eisenhower National System Of Interstate and Defense Highways". Federal Highway Administration. December 31, 2016. Retrieved December 22, 2017.

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