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.
List of Interstate Highways in Maryland
The following is a list of Interstate Highways in Maryland. There are currently 16 Interstate Highways that exist entirely or partially in the U.S. state of Maryland. Six of these are primary Interstates while ten are auxiliary Interstates related to one of the primary Interstates. The longest primary Interstate in Maryland is Interstate 95 (commonly abbreviated I-95) at . The shortest primary Interstate in Maryland is I-81 at . I-97 is the shortest primary Interstate at and the shortest intrastate Interstate. I-97 is also the only primary Interstate to be located entirely within one county and to not connect with any other primary Interstate. The longest auxiliary Interstate in Maryland is I-695 at . The shortest auxiliary Interstate in Maryland is I-295 at . All Interstates are maintained by the Maryland State Highway Administration except for all of I-395, all of I-895, a small part of I-695, I-95 within and north of Baltimore, and I-83 within Baltimore. Maryland has one unsigned Interstate, I-595; that highway is marked as U.S. Route 50 and US 301, which are concurrent with I-595 for its entire length. Maryland has one former Interstate, I-170, which is shaded in dark gray in the list.