Interstate 15

Interstate 15 is a major north–south Interstate Highway in the Western United States, traversing over 1,400 miles from the international border with Mexico near San Diego to the international border with Canada at Sweetgrass, Montana. It serves as a critical transportation corridor connecting the major metropolitan areas of Southern California, the Las Vegas Valley, and the Wasatch Front in Utah. The highway passes through diverse landscapes, including the Mojave Desert, the Colorado Plateau, and the Rocky Mountains, and is a vital route for commerce, tourism, and regional connectivity.

Route description

Beginning at its southern terminus at the Mexico–United States border near San Ysidro, it runs north through San Diego County, providing a key commuter route for communities like Escondido and Temecula. It crosses into the Inland Empire, serving the cities of San Bernardino and Ontario before ascending into the San Gabriel Mountains via Cajon Pass. After entering the Mojave Desert, it proceeds northeast across the state line into Nevada, where it passes through the resort city of Las Vegas and the community of Mesquite. The highway then cuts through the northwestern corner of Arizona near the Virgin River before entering Utah. In Utah, it serves the rapidly growing metropolitan areas of St. George, Provo, and Salt Lake City, running along the western front of the Wasatch Range. It continues north into Idaho, passing near Pocatello and Idaho Falls before entering Montana. In Montana, it travels through Butte, Helena, and Great Falls on its way to the Port of Sweetgrass at the Canada–United States border.

History

The route's alignment generally follows several historically significant corridors, including early Native American trails, the path of the Mormon Trail used by settlers of The Church of Jesus Christ of Latter-day Saints, and segments of historic auto trails like the Arrowhead Trail. Its designation as part of the Interstate Highway System was authorized by the Federal-Aid Highway Act of 1956. Construction proceeded in segments throughout the 1960s and 1970s, with challenging engineering feats required in areas like the Virgin River Gorge in Arizona and through the mountainous terrain of Montana. Major upgrades and expansions, such as the addition of HOV lanes in San Diego County and the reconstruction of interchanges in the Las Vegas Valley, have continued into the 21st century to manage increasing traffic volumes.

Major intersections

From south to north, key junctions include its terminus at Interstate 5 in San Diego and interchanges with Interstate 10 in Ontario and Interstate 40 in Barstow. In Nevada, it intersects with Interstate 215 and U.S. Route 95 in Las Vegas. Within Utah, it has major junctions with Interstate 70 near Cove Fort, Interstate 80 in Salt Lake City, and Interstate 84 near Tremonton. In Idaho, it meets Interstate 86 at Pocatello and U.S. Route 20 at Idaho Falls. Key intersections in Montana include junctions with Interstate 90 at Butte and Interstate 115 near Helena, culminating at the border crossing into Alberta.

Auxiliary routes

Several three-digit auxiliary Interstate Highways branch from it to serve metropolitan areas and provide bypass routes. These include Interstate 215 in San Bernardino County, Interstate 215 in Clark County, and Interstate 515 in Nevada. In Utah, Interstate 215 forms a belt route around Salt Lake City, while Interstate 315 is a short spur in Billings. Other notable business loops and spurs serve cities like Las Vegas, Mesquite, Salt Lake City, Ogden, and Great Falls.

See also

* List of Interstate Highways * Pan-American Highway * U.S. Route 91 * Transportation in the United States * California State Route 15 * Montana Highway 15

Category:Interstate 15 Category:Interstate Highways in Arizona Category:Interstate Highways in California Category:Interstate Highways in Idaho Category:Interstate Highways in Montana Category:Interstate Highways in Nevada Category:Interstate Highways in Utah