Interstate 5 (I-5) is the main north–south Interstate Highway on the West Coast of the United States, running largely parallel to the Pacific Coast of the contiguous U.S. from Mexico to Canada. It travels through the states of California, Oregon, and Washington, serving several large cities on the West Coast, including San Diego, Los Angeles, Sacramento, Portland, and Seattle. It is the only continuous Interstate highway to touch both the Mexican and Canadian borders. Upon crossing the Mexican border at its southern terminus, the highway continues to Tijuana, Baja California, as Mexican Federal Highway 1 (Fed. 1). Upon crossing the Canadian border at its northern terminus, it continues to Vancouver as British Columbia Highway 99 (BC 99).

The San Ysidro Port of Entry is the largest land border crossing between San Ysidro and Tijuana, and the fourth-busiest land border crossing in the world with 70,000 northbound vehicles and 20,000 northbound pedestrians crossing each day, in addition to southbound traffic. It connects Mexican Federal Highway 1 on the Mexican side with Interstate 5 on the American side. The San Ysidro Port of Entry is one of three ports of entry in the San Diego–Tijuana metropolitan region.