Interstate 15 (I-15) is the fourth-longest north–south Interstate Highway in the United States, traveling through the states of California, Nevada, Arizona, Utah, Idaho, and Montana from San Diego to the Canadian border. The Idaho, Utah and Arizona portions have been officially designated the "Veterans Memorial Highway".

Since I-15's inception, it has served as a long-haul route for North American commerce. It is now officially chartered for this purpose. From the junction of Interstate 515 in Las Vegas to the Canadian border, I-15 forms part of the CANAMEX Corridor, a High Priority Corridor, as a result of the North American Free Trade Agreement.

Local portions were built to connect the Inland Empire with San Diego in California, facilitate tourism access to Las Vegas, interconnect all of the Metropolitan Statistical Areas in Utah except Logan, and provide freeway bypasses for Pocatello, Idaho Falls, and Great Falls.

Since I-15's initial construction, California, Nevada, and Utah have consistently ranked in the fastest growing areas of the United States. As a result, the I-15 corridor has substantially increased in population and commuter traffic has increased the traffic burden on the freeway. Current population estimates are that more than 75 percent of Utah's population, 19 percent of California's population, and more than 70 percent of Nevada's population live in counties where Interstate 15 is the primary transportation corridor. Similarly, in California, I-15 is seeing more commuter traffic due to the growth of the Mojave Desert communities of Hesperia and Barstow, California. In all of these states, I-15 has recently been or is currently in the process of being upgraded to increase capacity. The Arizona, Idaho and Montana portions have retained their rural, long-haul character. Although Arizona has also grown substantially since I-15's inception, I-15 only serves an isolated corner of the state.