Interstate 15 (I-15) is a major Interstate Highway in the Western United States, running through Southern California and the Intermountain West. I-15 begins near the Mexican border in San Diego County and stretches north to Alberta, Canada, passing through the states of California, Nevada, Arizona, Utah, Idaho, and Montana. The Interstate serves the cities of San Diego, San Bernardino, Las Vegas, Salt Lake City, Idaho Falls, and Great Falls. It also passes close to the urban areas of Los Angeles, Orange, and Riverside counties, California. The stretches of I-15 in Idaho, Utah, and Arizona have been designated as the "Veterans Memorial Highway". The southern end is at a junction with I-8 and State Route 15 (SR 15) in San Diego, and the northern end is at a connection with Alberta Highway 4 at the Sweetgrass–Coutts Border Crossing.

The Dwight D. Eisenhower National System of Interstate and Defense Highways, commonly known as the Interstate Highway System, or the Eisenhower Interstate System, is a network of controlled-access highways that forms part of the National Highway System in the United States. The system extends throughout the contiguous United States and has routes in Hawaii, Alaska, and Puerto Rico.