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.