California State Route 123

Route 123 is a four-lane boulevard with a median strip for its entire length. Its southern terminus is at the underpass of Interstate 580 in Oakland. Going north, it passes through the cities of Emeryville, Berkeley, Albany, and El Cerrito. It briefly turns on Cutting Boulevard before entering Richmond at its northern terminus under Interstate 80.

San Pablo Avenue is sometimes used as an alternate route to the Eastshore Freeway (Interstate 80) when that freeway becomes very congested. Major intersections along this route include 40th Street, Ashby Avenue (State Route 13), University Avenue (which leads to UC Berkeley), Gilman Street, Marin Avenue, Central Avenue and Cutting Boulevard.

Continuing on San Pablo Avenue past Route 123's southern terminus eventually leads to downtown Oakland and Oakland City Hall where San Pablo Avenue ends. Continuing on San Pablo Avenue before Route 123's northern terminus leads to the cities of San Pablo, Pinole, Hercules, Rodeo, and Crockett. In Hercules, San Pablo Avenue meets the terminus of State Route 4 near Interstate 80, and, after a discontinuity bridged by Parker Avenue in Rodeo, the road approaches the Carquinez Bridge and arrives in Crockett as Pomona Street.

An AC Transit Rapid Bus (72R-San Pablo Rapid) runs along San Pablo Ave. from Downtown Oakland to Contra Costa College in San Pablo. The express bus line was put in place after a Metropolitan Transportation Commission study determined that it would be more cost-effective than a previous proposal to install light rail along the route. The BART system runs its Richmond leg parallel to the route up to the El Cerrito Del Norte station.

Route shield signs at the intersection of San Pablo Avenue (SR 123) and Ashby Avenue (State Route 13) in Berkeley.

The Alvarado Adobe is located by the San Pablo City Hall on the corner of San Pablo Avenue and Church Lane.

SR 123 is part of the National Highway System,[2] a network of highways that are considered essential to the country's economy, defense, and mobility by the Federal Highway Administration.[3]

San Pablo Avenue is one of the oldest existing roads in the East Bay. It originated in the Spanish colonial era as the Camino de la Contra Costa ("road of the opposite shore", i.e. opposite from the Presidio of San Francisco and the settlement around the Mission in San Francisco) and was legally a "camino real"[4] ("royal road", i.e., property of the Spanish crown) until Mexico won its independence in 1821. It ran from the Encinal ("Oakland") landings of the Rancho San Antonio northward (actually northwestward) along the bayshore, then eastward just inland of the Carquinez Strait. It was the principal thoroughfare for the scattered ranches throughout this part of the East Bay.

The name persisted into the American era when it was still called the "Contra Costa Road". On July 15, 1852, the Court of Sessions of Contra Costa County ordered the construction of a more direct and somewhat improved road along the same general route between the Rancho San Pablo and Oakland,[5] which consequently became known as "The San Pablo Road". This segment subsequently became today's "San Pablo Avenue".

In 1927, this road was designated as part of the Lincoln Highway, the nation's first transcontinental road upon the opening of the new highway bridge across the Carquinez Strait.

Prior to the construction of the Eastshore Highway, San Pablo Avenue was the main north–south route through the northern East Bay, carrying the designation U.S. Route 40 north of University Avenue in Berkeley (US 40 proceeded down to the foot of University and the end of the Berkeley Pier where an auto ferry transported motorists to the Hyde Street Pier in San Francisco). U.S. 40 was moved to the new highway after it was built (1930s), and about 25 years later took its current designation of Interstate 80. San Pablo Avenue was Business U.S. 40 until 1964.

During 2005–06, San Pablo Avenue was repaved and otherwise rehabilitated by Caltrans. Portions of San Pablo Avenue, particularly in Berkeley, Albany, and El Cerrito, are slowly transforming, with a mix of trendy shops, restaurants and condominium developments.

In the early part of the 20th century, a streetcar line ran on San Pablo between Richmond and Oakland. Part of the Oakland segment of these tracks up to Grayson Street in Berkeley were used during World War II for the Shipyard Railway of the Key System which transported workers from the Key System's hub in Emeryville to the Kaiser Shipyards in Richmond.

Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, based on the alignment that existed at the time, and do not necessarily reflect current mileage. R reflects a realignment in the route since then, M indicates a second realignment, L refers an overlap due to a correction or change, and T indicates postmiles classified as temporary (for a full list of prefixes, see the list of postmile definitions).[1] Segments that remain unconstructed or have been relinquished to local control may be omitted. The numbers reset at county lines; the start and end postmiles in each county are given in the county column.

County	Location	Postmile [1][6][7]	Destinations	Notes
Alameda ALA 0.00-5.18	Oakland	0.00	San Pablo Avenue	Continuation beyond I-580
		0.00	I-580 east (MacArthur Freeway) to SR 24 – Hayward, Stockton, Walnut Creek	Interchange; south end of SR 123
	Berkeley	1.91	SR 13 (Ashby Avenue)
		3.15	University Avenue	Serves UC Berkeley
Contra Costa CC 0.00-2.20	El Cerrito	0.29	Central Avenue
		2.10	San Pablo Avenue, Cutting Boulevard	San Pablo Avenue was former US 40 east
	Richmond	2.20	I-80 east (Eastshore Freeway) – Sacramento	Interchange; north end of SR 123
		2.20	Cutting Boulevard – Point Richmond	Continuation beyond I-80
1.000 mi = 1.609 km; 1.000 km = 0.621 mi

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Wikimedia Commons has media related to California State Route 123.

• Caltrans: Route 123 Highway Conditions
• California Highways: Route 123
• AARoads: State Route 123