Interstate 8 (I-8) is an Interstate Highway in the southwestern United States. It runs from the southern edge of Mission Bay at Sunset Cliffs Boulevard in San Diego, California, almost at the Pacific Ocean, to the junction with I-10, just southeast of Casa Grande, Arizona. In California, the freeway travels through the San Diego metropolitan area as the Ocean Beach Freeway and the Mission Valley Freeway before traversing the Cuyamaca Mountains and providing access through the Imperial Valley, including the city of El Centro. Crossing the Colorado River into Arizona, I-8 continues through the city of Yuma across the Sonoran Desert to Casa Grande, in between the cities of Phoenix and Tucson.

In the U.S. state of Arizona, Interstate 10 (I‑10), the major east–west Interstate Highway in the United States Sun Belt, runs east from California, enters Arizona near the town of Ehrenberg and continues through Phoenix and Tucson and exits at the border with New Mexico near San Simon. The highway also runs through the cities of Casa Grande, Eloy, and Marana. Segments of the highway are referred to as either the Papago Freeway, Inner Loop, or Maricopa Freeway within the Phoenix area and the Pearl Harbor Memorial Highway outside metro Phoenix.