In 1956, the route of what would become the South Bay Freeway had been determined; it would run from Sweetwater Road in National City to Spring Valley and the intersection of Sweetwater Road and Jamacha Boulevard. Three years later, the California State Legislature added Route 280 from near the Sweetwater River to El Cajon to the state highway system. The South Bay Freeway was included in the county's 1960–1961 budget as the most important project. By 1961, E Street in Chula Vista continued along the Sweetwater River; it turned northeast and became Sweetwater Road before it entered into Lemon Grove.