High Quality Content by WIKIPEDIA articles! U.S. Route 91 is a north–south United States highway. The highway currently serves as a connection between the Cache Valley area of Utah and Idaho to the Salt Lake and Idaho Falls population centers. Prior the mid-1970s, U.S. 91 was an international commerce route from Long Beach, California to the Canadian border north of Sweetgrass, Montana. The highway served as the main street of most of the communities it served, including Las Vegas Boulevard in Las Vegas and State Street in Salt Lake City. The route has been largely replaced by Interstate 15. A portion of the highway`s former route in California is currently State Route 91.