SR 55 was first added to the state highway system in 1931, known as part of Legislative Route 43, and was routed on surface streets. It was renumbered SR 55 in 1959, and the construction of the freeway portion began in the 1960s and continued until 1992. Due to congestion, several alternatives are being discussed to expand the freeway portion past its current end in Newport Beach. SR 55 received the first carpool lane in Orange County in 1985, and the first direct carpool ramp in 1995.