U.S. Route 90
U.S. Route 90 (US 90) is an east–west United States highway. Despite the "0" in its route number, US 90 never was a full coast-to-coast route; it has always ended at Van Horn, Texas with the exception of a short-lived northward extension to US 62/US 180 near Pine Springs, Texas which lasted less than a year, and the signs on that segment were changed to Texas State Highway 54, traveling from Interstate 10 (I-10) at exit 140A and heading to its northern terminus at US 62/US 180.
Interstate 90
Near Rapid City at the Wyoming border I-90 is a four-lane divided highway with a grass median. In the Sioux Falls area, I-90 intersects I-29 and continues east a short distance to Minnesota. I-90 is the longest east–west thoroughfare in South Dakota. This interstate goes through Mitchell, Sioux Falls, and Rapid City. It does not go through the state capital of Pierre.