Interstate 405 Washington
Interstate 405 north at Downtown Bellevue, Washington. 06/27/15
Overview
Interstate 405 provides a bypass to the east of Seattle, connecting with several major suburbs on the east shore of Lake Washington. The urban loop is the most direct route to Redmond, home of Microsoft, via the freeway along State Route 520. As a result of growth in the greater Seattle area, Interstate 405 carries significant traffic volume, almost on a level like I-405 in California, albeit with fewer lanes.
High Priority Corridor
Interstate 405 is part of High Priority Corridor 35: FAST Corridor.
History
The original proposal for Interstate 405 around greater Seattle was submitted to the American Association of State Highway Officials (AASHO) in a letter dated July 14, 1958.1 Initial stretches were designated as Washington State Route 405 between Renton and Tukwilla. The first section opened to traffic in September 1965. SR 405 was redesignated as I-405 with its completion by 1971.2
Interstate 405 completed north to Bellevue on the 1967 Official Washington Highway Map
Route Information
Source: December 31, 2021 Interstate Route Log and Finders List
I-405 Annual Average Daily Traffic (AADT)
Source: 2017 AADT – WSDOT Traffic Data Geoportal
State named trailblazers for I-5 and I-405 along the eastbound entrance ramp to SR 518 from Seattle-Tacoma International Airport (SEA). Photo by Jeff Royston (02/24/06).
SR 509 south at the eastbound on-ramp for SR 518 to Seattle-Tacoma International Airport (SEA) and I-5/405. Photo by Chris Elbert (03/03/06).
Interstate 405 temporary designated as State Route 405 north of Bellevue in 1967
 Photo Guides
North End
– Lynnwood, Washington
North at
South at
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North at
North End Throwback
North at
South at
South End
– Tukwila, Washington
South at
East at
A left exit connects SR 518 east with I-5 north into Seattle. A lane drop occurs at the ramp for I-5 south to Tacoma while a single lane transitions onto Interstate 405 north to Renton. 07/20/23
North at
South at
South End Throwback
Sources:
- Washington State Highway Commission letter to AASHO, dated July 14, 1958, retrieved from AASHTO Route Numbering Archive.
- Interstate 405 (Washington). AARoads Wiki.
Page updated February 1, 2024