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 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 is a north–south freeway that serves as a bypass of I-5 through Seattle while serving the Eastside region. It is listed as part of the National Highway System, identifying routes that are important to the national economy, defense, and mobility, and the state's Highway of Statewide Significance program, recognizing its connection to major communities. The highway is maintained by the Washington State Department of Transportation (WSDOT), who conduct an annual survey of traffic volume that is expressed in terms of average annual daily traffic (AADT), a measure of traffic volume for any average day of the year. Average daily traffic volumes on I-405 in 2016 ranged from a minimum of 76,000 at its southern terminus in Tukwila to 209,000 in Downtown Bellevue. Approximately 86 percent of peak-direction lane miles on I-405 are rated as "routinely congested" by WSDOT and the highway accounted for over 30 percent of delays on the Seattle area's urban freeways from 2013 to 2017. The freeway has a system of high-occupancy vehicle lanes (HOV lanes) from Tukwila to Downtown Bellevue that become high-occupancy toll lanes (HOT lanes) from Bellevue to Lynnwood. The HOT lanes are controlled through