List of Interstate Highways in Washington
Interstate 90 (I-90) is the longest primary Interstate Highway in Washington, which connects Seattle to Spokane and the Idaho border, measuring , while I-82, connecting the Oregon border city of Umatilla to Elensburg via Yakima, is the shortest at . The longest auxiliary Interstate Highway in Washington is I-405, a bypass of Seattle through the Eastside, at , and the shortest is I-705, a spur into downtown Tacoma, at . One route, I-605, has been proposed over the years to form another Eastside bypass, however there are no plans to construct this fifth auxiliary route.
After passage of the Federal Aid Highway Act of 1956, which formed the Interstate Highway System, the American Association of State Highway Officials had approved I-5 and I-90 across Washington on August 17, 1957. I-82 was approved on October 17, 1957, two months after I-5 and I-90, as part of a addition to the Interstate Highway System.
Interstate 57
In the state of Illinois, Interstate 57 runs from the bridge over the Mississippi River north to Chicago. I-57 is the longest Interstate Highway in Illinois. Its route follows essentially the earlier route of US 51 in southernmost Illinois (US 51 has been diverted to I-57 where I-57 has always been close to old US 51 between Future City and Dongola) before taking a northeastward diagonal to Illinois 37, which remains intact as a town-to-town through route, past its interchange with Interstate 24 (the northwestern terminus of Interstate 24) near Pulleys Mill and a short duplex with Interstate 64 near Mount Vernon north to Effingham, where it has a short concurrence with Interstate 70. It then follows US 45 bypassing cities of Champaign and Urbana (where it meets Interstates 72 and 74), and heads north to Onarga whereafter it follows the formerly duplex path of US 45 and (now decommissioned in most of Illinois) old US 54 to Kankakee. At Kankakee it heads northward largely parallel to the now decommissioned route of old US 54 (since renumbered largely as Illinois 50) into the Chicago area, meeting Interstate 80 in Hazel Crest, Interstate 294 in Blue Island, and feeding Interstate 94 on Chicago's South Side.