state to measure traffic volume. This is expressed in terms of average annual daily traffic (AADT), which is a measure of traffic volume for any average day of the year. In 2013, WSDOT calculated that the busiest section of SR 526 was its interchange with Evergreen Way, carrying 75,000 vehicles, while the least busiest section of the highway was its western terminus at SR 525, carrying 8,500 vehicles. SR 526 is designated as part of the National Highway System for its whole length, classifying it as important to the national economy, defense, and mobility. WSDOT designates the entire route of SR 526 as a Highway of Statewide Significance, which includes highways that connect major communities in the state of Washington. History SR 526 was established during the 1964 state highway renumbering as the successor to SSH 1I between Mukilteo and Everett. The highways were preceded by the Mukilteo-Everett wagon road that was opened on August 14, 1914, traveling east along Possession Sound between Mukilteo and Everett, later renamed to Mukilteo Boulevard during the 1920s. The boulevard route had previously been surveyed in 1882 for a wagon road connecting Mukilteo to Lowell (now part of Everett) by the county government. SSH 1I was designated in 1937 along the route of Mukilteo Boulevard and a new highway connecting Mukilteo to U.S. Route 99 (US 99) in Lynnwood, traveling in a circular arc. SSH 1I was split into SR 525 from Lynnwood to Mukilteo and SR 526 from Mukilteo to Everett during the 1964 state highway renumbering. The eastern terminus of SR 526, an interchange with I-5 in Everett, was completed in February 1965 and later became the southern terminus of SR 529 until 1991. The interchange was later converted to a single-point urban interchange in 2007 as part of a WSDOT project to improve I-5 through Everett. SR 526 was realigned onto its current alignment during construction of the Boeing factory in 1967. The route initially used Casino Road, which was a two-lane road between Nelsons Corner in Mukilteo and Beverly Park in Everett; the eastern terminus was located at its intersection with US 99. The road was plagued with severe congestion as it was the only major arterial serving the factory at the time; Boeing's selection of the factory site was contingent on the road's reconstruction into a four-lane highway. However, the federal Economic Development Administration denied Everett's request for a