California State Route 55

State Route 55 (SR 55) is an 18-mile (30-km) long north–south highway in the U.S. state of California. The portion of the route built to freeway standards is known as the Costa Mesa Freeway (formerly the Newport Freeway). SR 55 runs between Finley Avenue south of Pacific Coast Highway (SR 1) in Newport Beach and the Riverside Freeway (SR 91) in Anaheim to the north, intersecting other major Orange County freeways such as SR 22, SR 73, and Interstate 405 (I-405). The freeway passes through suburban Orange County.

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.