SR 54 was extended west as a freeway to I-5 from I-805 at the same time the Sweetwater River flood control channel was built; the state proposed routing the flood channel in between the two roadways of the freeway in 1963, and it would also delineate the boundary between the cities of Chula Vista and National City. Later that year, the county proposed an extension of the freeway east to US 80 and Third Street in El Cajon. In 1966, the U.S. Army's Board of Engineers supported the construction of the flood channel, to protect future development in the surrounding region from floods; the integration of SR 54 was included in the proposal.