Interstate 405 marker

Interstate 405
I-405 highlighted in red
Route information
Auxiliary route of I-5
Defined by RCW 47.17.595
Maintained by WSDOT
Length30.30 mi[1][2] (48.76 km)
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
CountiesKing, Snohomish
Highway system
SR 401SR 409

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.

Route description

I-405 begins as a continuation of State Route 518 (SR 518) at a junction with Interstate 5 in Tukwila, northeast of Seattle–Tacoma International Airport. It gains a set of high-occupancy vehicle lanes (HOV lanes) and travels east around the Southcenter Mall and Tukwila's retail district as an eight-lane freeway. I-405 crosses the Green River and intersects Interurban Avenue and SR 181 near the Tukwila train station and Starfire Sports complex. The freeway enters the city of Renton and travels between a waste treatment plant and the former Longacres racetrack (now a Boeing office park),[3] crossing over a major railroad used by BNSF and Union Pacific. After crossing the Black River and passing through suburban office parks, the highway intersects SR 167 (the Valley Freeway) and Rainier Avenue in a cloverleaf interchange and begins to turn north towards downtown Renton.[4]

The freeway enters a series of "s-curves" as it approaches downtown Renton,[5] turning north after intersecting SR 515 at Talbot Road in a half-diamond interchange and continuing northeast along the underside of Renton Hill.[6] After crossing the Cedar River near the Renton Public Library, I-405 passes through a public park and intersects SR 169 and SR 900 at two separate interchanges, beginning a short concurrency with the latter. The freeway passes the Kenworth truck plant and the Renton Landing shopping center near the Boeing Renton Factory[citation needed] before reaching a second junction with SR 900, which continues east towards Issaquah.[4]

Climbing Kennydale Hill,[5] I-405 intersects N 30th St and Kennewick Place NW, which serves north Renton, and Kennydale, before quickly descending to another hybrid diamond/partial cloverleaf interchange with NE 44th Street, which provides access to Newcastle. I-405 now closely follows Lake Washington, and enters a wooded section until an interchange with Lake Washington Boulevard and 112th Ave SE which serves both a park and ride station and the community of Newport Hills. The final interchange before I-90 is a diamond interchange serving Coal Creek Parkway.

I-405 heading into downtown Bellevue

Factoria Mall is east of I-405 as it approaches a full stack interchange with Interstate 90 which provides access to Seattle, Mercer Island, as well as the Eastgate neighborhood of Bellevue and Issaquah. Mercer Slough is west of I-405 as it heads towards downtown Bellevue. A 2008 construction project demolished the Wilburton Tunnel which formerly covered a portion of the freeway between Factoria and Bellevue.[7]

I-405 passes the historic Wilburton Trestle near a diamond interchange with SE 8th Street that connects the freeway to South Bellevue and the Lake Hills area. In quick succession is a short diamond interchange with NE 4th Street, a full cloverleaf with NE 8th Street, serving downtown Bellevue and Overlake Medical Center, and an HOV only left exit to the Bellevue Transit Center at NE 6th Street. The freeway's set of four high-occupancy toll lanes (HOT lanes) begin at the NE 6th Street ramp, traveling north with limited entry and exit points. SR 520 which provides access to Seattle, Medina, the Microsoft campus, and Redmond, is the next interchange, with a half cloverleaf interchange that includes several fly-over ramps to allow complete access to and from SR 520.

Bridle Trails State Park borders the freeway on the east side, while Watershed Park and Northwest University are on the western side of the freeway as it approaches NE 70th Place, serving Houghton and Snyders Corner before approaching a full cloverleaf with former SR 908 serving Kirkland. An incomplete interchange with NE 116th Street comes before I-405 connects to Totem Lake via an interchange with NE 124th Street and an HOV only left exit to the Evergreen Hospital and NE 128th Street. NE 160th Street is the next interchange before I-405 crosses over the Sammamish River and connects to SR 522 which provides access to downtown Bothell and Woodinville. An interchange with NE 195th Street provides access to the local business park and the University of Washington Bothell branch.

I-405 in Snohomish County

Entering Snohomish County at mile post 25, I-405 enters a wooded area before coming to an interchange with the Bothell-Everett Highway (SR 527), which is the final interchange before I-405 terminates at an interchange between Interstate 5 and SR 525.[4]

As of 2007, the most heavily traveled section of I-405 is near SE 8th Street in downtown Bellevue, with a daily average of 200,000 cars per day traveling through this segment.[8] This number was slightly lower in 1997, with 190,000 cars per day,[9] but has dramatically increased since the first measurement in 1967, with 32,600 cars per day traveling through Bellevue.[10]


The first road connecting most of the eastside communities, Secondary State Highway 2A (SSH 2A),[11] was already in existence since at least 1927. SSH 2A connected US 10 and US 410 in Renton to the north, through Kirkland and Bothell, connecting back to US 99 in Everett.[12] In 1964, the system of Primary and Secondary state highways was removed in favor of signed routes, and PSH 2A was renumbered SR 405. The first segment of the interstate to be completed was between Tukwila and Renton, opening to traffic on August 31, 1965.[13] By 1971, SR 405 was renumbered to Interstate 405 after it was completely improved to Interstate Highway standards.[citation needed]

One of the major construction projects on the highway was straightening the s-curves in Renton. This project began in 1990, and was estimated to cost $70 million. Also during this time the portion of the highway between I-5 and South Renton was being repaved and HOV lanes were being added.[14]

On September 27, 2015, a set of high-occupancy toll lanes (HOT lanes) opened on I-405 between Bellevue and Lynnwood, replacing the existing HOV lanes from NE 6th Street to I-5/SR 525.[15][16]


Originally intended as a bypass to I-5 through Seattle, I-405 has experienced a large increase in traffic volume since its construction. I-405 is now the most congested freeway in Washington State, particularly the segment between State Route 169 and I-90.[17]

Currently underway is the Nickel Project, which in 2003 originally included three planned improvements for I-405:[18]

  • The construction of one lane in each direction between SE 8th and I-90, replacing the Wilburton Tunnel.
  • The construction of one northbound lane from NE 70th to NE 124th, and one southbound lane from SR 522 to SR 520.
  • The construction of one northbound lane from SR 181 to SR 167, and one southbound lane from SR 169 to SR 167.

In 2005, the "Renton to Bellevue Project" was added as part of the Nickel Project,[19] and would have added two lanes in each direction between SR 169 and I-90. However, in November 2007, voters rejected the ballot measure which would have provided the additional funds necessary for this project. At this time the project is still largely unfunded.[17] The web site "Road to Ruin" ranks the widening of I-405 as the fourth most wasteful highway project in the United States. The project is designed to help traffic move more smoothly on I-405.[20]

A bus rapid transit line is planned to run along nearly the entirety of I-405 as part of the Sound Transit 3 ballot measure that was approved by voters in 2016. The project involves reconfiguring the extant cloverleaf interchange at Northeast 85th Street in Kirkland to include separate bus ramps built for access to and from the planned Northeast 85th Street station.[21]

Exit list

KingTukwila0.000.00 SR 518 west – Burien, Sea-Tac AirportContinuation beyond I-5
0.000.00 I-5 – Seattle, Tacoma, PortlandSouthbound exit and northbound entrance; I-5 exit 154 northbound, 154A southbound
0.340.55Southcenter Boulevard – Southcenter MallSouthbound exit and northbound entrance
0.961.541 SR 181 south (West Valley Highway) – Tukwila
Renton2.303.702 SR 167 (Rainier Avenue South) – Renton, AuburnSigned as exits 2A (south) and 2B (north) southbound
2.964.763 SR 515 (Talbot Road South)Southbound exit and northbound entrance
4 SR 169 south / SR 900 west (Bronson Way) – Renton, Maple Valley, EnumclawSouthern end of SR 900 concurrency
5.378.645 SR 900 east (Sunset Boulevard Northeast) / Park Avenue North – IssaquahNorthern end of SR 900 concurrency
6.4810.436Northeast 30th Street
7.4411.977Northeast 44th Street
Bellevue9.2314.859112th Avenue Southeast – Newcastle
10.1516.3310Coal Creek Parkway / Factoria Boulevard Southeast
11.0217.7311 I-90 – Spokane, Seattle
12.7620.5412Southeast 8th Street / 116th Avenue Northeast
13.5421.7913ANortheast 4th Street
13.6822.02Northeast 6th StreetHOV and toll access only
13.8122.2313BNortheast 8th Street
14.8223.8514 SR 520 – Seattle, Redmond
Kirkland17.4328.0517Northeast 70th Place
18.0829.1018Northeast 85th Street – Redmond, Kirkland
19.8231.9020ANortheast 116th StreetNorthbound exit and southbound entrance
20.3032.6720BNortheast 124th Street / Totem Lake BoulevardSigned as exit 20 southbound
20.6433.22Northeast 128th StreetHOV and toll access only
22.6136.3922Northeast 160th Street
Bothell23.5237.8523 SR 522 to US 2 – Bothell, Kenmore, WoodinvilleSigned as exits 23A (east) & 23B (west) southbound
24.4639.3624Northeast 195th Street / Beardslee Boulevard
Snohomish26.7343.0226 SR 527 – Bothell, Mill Creek
30.3048.76 I-5 – Lynnwood, Seattle, Everett, Vancouver B.C.Northbound exit and southbound entrance; I-5 exit 182
30.3048.76 SR 525 north – MukilteoContinuation beyond I-5
1.000 mi = 1.609 km; 1.000 km = 0.621 mi


  1. ^ a b "State Highway Log - Planning Report - SR 2 to SR 971" (PDF). Washington State Department of Transportation. 2006. Archived from the original (PDF) on April 10, 2008. Retrieved August 16, 2008.
  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.
  3. ^ Lane, Polly; Smith, Sara (September 27, 1990). "Boeing Buys Longacres-- Site May Be Company Headquarters; Some Racing Possible Elsewhere". The Seattle Times. Retrieved September 27, 2008.
  4. ^ a b c Google (January 6, 2019). "Interstate 405" (Map). Google Maps. Google. Retrieved January 6, 2019.
  5. ^ a b Gilmore, Susan (June 30, 2002). "Straight talk on S-curves, traffic lingo". The Seattle Times. p. B1. Retrieved September 28, 2008.
  6. ^ City of Renton Designated Neighborhoods (PDF) (Map). City of Renton. November 2014. Retrieved January 6, 2019.
  7. ^ "I-405 lane closures, other traffic headaches loom this weekend". Seattle Times. August 15, 2008. Retrieved August 16, 2008.
  8. ^ "2007 Annual Traffic Report" (PDF). Washington Department of Transportation. Archived from the original (PDF) on March 26, 2009. Retrieved August 16, 2008.
  9. ^ "1997 Annual Traffic Report" (PDF). Washington Department of Transportation. Retrieved September 27, 2008.
  10. ^ "1970 Annual Traffic Report" (PDF). Washington Department of Transportation. Archived from the original (PDF) on June 25, 2008. Retrieved September 27, 2008.
  11. ^ "40 Years With the Washington State Department of Highways" (PDF). Washington State Department of Transportation. Archived from the original (PDF) on October 30, 2008. Retrieved September 28, 2008.
  12. ^ Official Auto Tails map, Washington, Oregon (Map). Rand McNally. 1927. Seattle and Vicinity inset. Retrieved September 27, 2008.
  13. ^ "3 Miles of Renton Freeway Opened". The Seattle Times. August 31, 1965. p. 6.
  14. ^ Aweeka, Charles (September 25, 1990). "S-Curves On I-405 To Be Set Straight -- First, Water Pipes Will Be Rerouted". The Seattle Times. Retrieved September 28, 2008.
  15. ^ "I-405 express toll lanes will open on Sept. 27" (Press release). Washington State Department of Transportation. August 20, 2015. Retrieved September 27, 2015.
  16. ^ Lindblom, Mike (September 19, 2015). "Q&A: a guide to using I-405's new express toll lanes". The Seattle Times. Retrieved September 27, 2015.
  17. ^ a b "I-405 - Renton To Bellevue Project SR 169 to I-90". Washington State Department of Transportation. Retrieved April 7, 2007.
  18. ^ "Nickel Funding Package Enacted for Transportation by the Washington State Legislature" (PDF). Washington State Department of Transportation. Retrieved December 6, 2007.
  19. ^ "I-405 New 2005 Funded Projects". Washington State Department of Transportation. Archived from the original on June 7, 2008. Retrieved December 6, 2007.
  20. ^ Taxpayers for Common Sense. "Road to Ruin" (PDF). Retrieved December 6, 2007.
  21. ^ Lindblom, Mike (September 6, 2018). "Sound Transit is taking a $300 million gamble on a new I-405 bus station in Kirkland". The Seattle Times. Retrieved January 23, 2020.

External links

Route map:

KML is from Wikidata
  • Media related to Interstate 405 (Washington) at Wikimedia Commons
  • WSDOT I-405 Corridor Program