U.S. Route 20 (US 20) is an east–west United States highway. The "0" in its route number indicates that US 20 is a coast-to-coast route. Spanning , it is the longest road in the United States, and the route roughly parallels that of Interstate 90 (I-90). There is a discontinuity in the official designation of US 20 through Yellowstone National Park, with unnumbered roads used to traverse the park.