SR 54 starts as a six-lane freeway from I-5 near the mouth of the Sweetwater River in National City. Both directions of the freeway are divided by the river; eastbound traffic traverses the south bank and westbound traffic traverses the north bank. The two sides join near the junction with I-805. The roadway continues east for several miles past the Westfield Plaza Bonita mall through suburban Paradise Hills in San Diego. As the freeway turns north in Bay Terraces, it merges with SR 125 north. The highways pass west of the Sweetwater Reservoir and Sweetwater Summit Regional Park, and the western segment of SR 54 ends at the Jamacha Boulevard exit in La Presa. Jamacha Boulevard veers northeast as an undivided highway through Spring Valley until it reaches Campo Road; it is only designated as County Route S17 (CR S17), while some maps do consider this part of SR 54.