The legislature added this road to the state highway system in 1933, and it became part of Legislative Route 11, which had stretched east from Sacramento along US 50. This part of Route 11 was not assigned a sign route number in 1934, but, by 1937, when the new Broadway Low Level Tunnel opened, it was part of Sign Route 24. That route had initially begun at Woodland and traveled northeast and east through the Feather River Canyon, and was extended southeast from Woodland along Sign Route 16 to Sacramento and then south and west via Antioch to the San Francisco – Oakland Bay Bridge approach in Berkeley. The California Freeway and Expressway System was formed in 1959, and included in the planned upgrades was the road between Antioch and Rio Vista. (North of Rio Vista the present SR 84 was part of the system.) The entire length was included in the State Scenic Highway System in 1963. In the 1964 renumbering, the Antioch-Sacramento roadway was split between two routes: Route 84 from Antioch to SR 12 near Rio Vista, and Route 160 from SR 12 to Sacramento. However, the entire route was marked as SR 160, and in 1981 the legislative definition was changed to reflect this.