State Route 54 (SR 54) is a state highway in the U.S. state of California that consists of two segments in San Diego County. The westernmost part of the highway is known as the South Bay Freeway, beginning at Interstate 5 (I-5) in National City and running along the Sweetwater River before ending at the intersection with SR 125 and Jamacha Boulevard near Spring Valley. SR 54 then resumes at SR 94 in Rancho San Diego as an undivided highway that leads to the city limits of El Cajon. County Route S17 (CR S17) connects the two portions of the highway; the center portion of SR 54 was never constructed.

Interstate 5 (I-5) is a major north–south route of the Interstate Highway System in the United States, stretching from the Mexican border at the San Ysidro crossing to the Canadian border near Blaine, Washington. The segment of I-5 in California runs 796.77 miles (1,282.28 km) across the length of the state from San Ysidro to the Oregon state line south of the Medford-Ashland metropolitan area. It is the longest interstate in California, and accounts for more than half of I-5's total length.