U. S. Route 101 in the state of California is one of the last remaining and longest U. S. Routes still active in the state, and the longest highway of any kind in California, US101 was also one of the original national routes established in 1926. Significant portions of US101 between the Los Angeles area and the San Francisco Bay Area follow El Camino Real, the road connecting the former Alta Californias 21 missions. US101 also has designated as the Santa Ana Freeway, Hollywood Freeway, Ventura Freeway, South Valley Freeway. This route is part of the California Freeway and Expressway System, the south terminus of US101 is in Los Angeles, about one mile east of downtown Los Angeles at the East Los Angeles Interchange, also known as the Commuters Complex. This southernmost portion is named the Santa Ana Freeway, inheriting that title as the extension of the roadway now known as I-5. From here, US101 becomes the Hollywood Freeway and it then heads to Hollywood and up through the Cahuenga Pass before reaching the San Fernando Valley. US101 then intersects with SR134 and SR170 at the known as the Hollywood Split. Here, the alignment of US101 shifts to the alignment of SR134, though confusing, the Hollywood Freeway name continues northward from this interchange on SR170, and the Ventura Freeway name continues eastward to SR134. From the Hollywood Split, US101 is an east–west highway and it meets with I-405 in Sherman Oaks, an interchange which holds claim to the most traveled intersection in the nation. Upon reaching Ventura, there is an interchange with SR126, North of Ventura, US101 switches intermittently between freeway and expressway status, but there are no traffic signals until San Francisco. From Ventura and through Santa Barbara, US101 closely follows the Pacific coastline until Gaviota State Park, at Gaviota State Park, the highway shifts back from an east–west highway to a north–south alignment. About one mile north of this point, US101 passes through the Gaviota Tunnel, a few miles north of the Gaviota Tunnel, SR1 splits from US101 and heads northwest, running along the Pacific coastline parallel and to the west of US101. US101 passes through Buellton, Los Alamos, Orcutt, Santa Maria, South of Santa Maria, US101 widens from a four-lane highway to a six-lane freeway. SR166 joins US101 for about 3 miles before splitting just north of the city limits, farther north, SR1 rejoins US101 between Pismo Beach and San Luis Obispo. Then US101 takes a route through the Salinas Valley, while Highway 1 heads northwest, running along the Pacific coastline in California, parallel. A steep segment between San Luis Obispo and Atascadero is known as the Cuesta Grade, North of Atascadero, the highway joins SR46 for about three miles through Paso Robles. From Paso Robles to Salinas, US101 is a known as the Salinas River Valley Highway
View northward from the Cahuenga Pass in 1972
Traffic descending the Cuesta Grade north of San Luis Obispo
US 101 sign in San Francisco
US 101 in San Francisco between Sacramento and Clay Streets; a Muni ETI Skoda bus can be seen in the background.