U.S. Route 101 (US 101) is a north–south United States Numbered Highway that runs between Los Angeles, California, and Tumwater, Washington. U.S. Route 101 in California covers approximately between the East Los Angeles Interchange and the Oregon border, making it the longest numbered route in California's highway network.
US 101 is a critical freeway in Greater Los Angeles and the San Francisco Bay Area; it is also a communal highway in the Central and North coasts, where it connects cities such as Santa Barbara, San Luis Obispo, Salinas, and Eureka. The Los Angeles portion of US 101 is one of the most congested freeways in the U.S. based on multiple studies. In the Central Coast, US 101 is a mix of freeway and expressway, while the North Coast segment is mostly a two-lane road with pockets of controlled-access configurations. The majority of the route is maintained by the California Department of Transportation (Caltrans).
US 101 was created in 1926, its route taking over or sharing paths with El Camino Real, Redwood Highway, and State Legislative Routes 1 and 2. US 101 originally continued south from Los Angeles, through Orange County and San Diego to the Mexican border, but this segment was switched to Interstate 5 (I-5) in 1964. Beginning in the 1930s, numerous US 101 segments were replaced or relocated, often to bypass smaller cities. In the 1940s and 1950s, many segments were upgraded to freeway standards, particularly in Southern California, San Jose, and along the San Francisco Peninsula. However, freeway upgrades were curtailed in the 1960s, and while a few sections have been upgraded since then, segments now are more commonly improved without being fully upgraded to freeway standards. In 2024, the Wallis Annenberg Wildlife Crossing, the world's largest wildlife crossing, began construction across US 101 in Ventura County. Proposed improvements yet to be implemented include two freeway caps in Los Angeles, trucking upgrades through Richardson Grove State Park, a tunnel in Del Norte County, and the addition of high-occupancy lanes in several areas.
US 101 and many of its features are known by various names. California residents generally refer to the route as "101" or "the 101" (pronounced "one-oh-one"), while segments in Los Angeles are variously named Santa Ana Freeway, Hollywood Freeway, and Ventura Freeway, and segments in the Bay Area are named South Valley Freeway, Bayshore Freeway, and Central Freeway. US 101 south of the Bay Area has been dedicated as El Camino Real, north of the Golden Gate Bridge as Redwood Highway, and the entire route is named both Blue Star Memorial Highway and Coast Highway. Several memorial and tourist designations have been applied to sections of the route. Segments of US 101 that run concurrently with California State Route 1 (SR 1) are also known as Pacific Coast Highway, sharing the name of that route.
Route description
US 101 runs for in California, making it the longest numbered route in the state. It is named Route 101 in Section 401 of the California Streets and Highways Code and defined as:
Route 101 is from: (a) Route 5 near Seventh Street in Los Angeles to Route 1, Funston approach, and, subject to Section 72.1, the approach to the Golden Gate Bridge in the Presidio of San Francisco via Santa Barbara, San Luis Obispo, and Salinas. (b) A point in Marin County opposite San Francisco to the Oregon state line via Crescent City.
The definition purposely omits the segment crossing the Golden Gate Bridge, as it is maintained by the Golden Gate Bridge, Highway and Transportation District and is not part of the state highway system. Despite this, U.S. Route logs from the American Association of State Highway and Transportation Officials (AASHTO) include the bridge as part of US 101, as do most other maps. The bridge, along with the rest of US 101, is also part of the National Highway System.
US 101 is part of the California Freeway and Expressway System, and portions of it are eligible for inclusion in the State Scenic Highway System. It is officially designated a scenic highway between Goleta and Las Cruces in Santa Barbara County and through Del Norte Coast Redwoods State Park in Del Norte County.
Southern California
US 101 begins in Boyle Heights at the East Los Angeles Interchange, a major freeway junction that includes I-5, I-10, and SR 60. The six-lane portion of the route is the northerly continuation of the Santa Ana Freeway, inheriting that name from I-5. After , US 101 turns west at the San Bernardino Split, a three-way junction with the San Bernardino Freeway that transitions into I-10 to the east. US 101 travels across the Los Angeles River before passing Los Angeles Union Station.
Proceeding in a generally northwestern direction, US 101 travels through downtown Los Angeles via the Downtown Slot between the Los Angeles Civic Center and El Pueblo de Los Ángeles, then intersects with SR 110 at the Four Level Interchange. Starting here, US 101 is named Hollywood Freeway. It bisects Echo Park, Silver Lake, Los Feliz, and Hollywood, passing Echo Park Lake, the Hollywood Boulevard Commercial and Entertainment District, and the Hollywood Bowl in the process. SR 2 has a short concurrency with the freeway within the area. North of Hollywood, US 101 traverses the Santa Monica Mountains via the Cahuenga Pass before entering the San Fernando Valley. It then passes Universal Studios Hollywood, after which it turns westward at the Hollywood Split, where it supersedes SR 134 on the Ventura Freeway while the Hollywood Freeway continues north as SR 170.
From the Hollywood Split, US 101 runs east–west despite its north–south designation. Because of this, the same freeway entrance can be signed as US 101 North and US 101 West or US 101 South and US 101 East; this is most common in the San Fernando Valley where local signage does not match Caltrans' statewide designation. Along this segment, US 101 intersects with I-405 in Sherman Oaks and SR 27 in Woodland Hills. In Calabasas, US 101 changes from heavily urbanized to a more rural character as it enters the Conejo Valley, where it transitions from Los Angeles County into Ventura County. In Thousand Oaks, US 101 and SR 23 run concurrently for about , between Westlake Boulevard and a three-way interchange with the Moorpark Freeway.
Continuing westward, US 101 climbs the Conejo Grade on a 7% incline before descending into the Oxnard Plain, where it has interchanges with SR 34 and SR 232 in Camarillo and Oxnard, respectively. Likewise in the latter city, SR 1 runs concurrently with US 101. Upon crossing the Santa Clara River, the highway enters Ventura, where it intersects with SR 126 and SR 33 on separate junctions.
Central Coast
The US 101/SR 1 duplex crosses the Ventura River at Emma Wood State Beach, at which point it borders the Pacific Coast for until Rincon Point; of this, the two routes run alongside rather than concurrent for , with the non-concurrent section of SR 1 routed on Rincon Parkway. The highway also passes through Faria, Mussel Shoals, and La Conchita along this stretch. After reaching Santa Barbara County, it intersects with SR 150—at this point, the Ventura Freeway name ends. US 101/SR 1 continues through Carpinteria, then returns to the coast for , passing through Summerland before entering Santa Barbara.
US 101/SR 1 bisects the entire length of Santa Barbara, with an interchange at SR 154. In Goleta, the highway has a junction with SR 217 that connects to University of California, Santa Barbara. West of Goleta, the routes narrow from six lanes to four and switch from freeway to expressway, then straddle a stretch of the Gaviota Coast, again often directly overlooking the shore.
At Gaviota, the highway curves sharply north and reverts to its original north–south orientation. It heads inland across the Santa Ynez Mountains via the Gaviota Pass, where northbound lanes pass through the Gaviota Tunnel—no tunnel exists in the southbound direction. About north of the Gaviota Tunnel, SR 1 splits from US 101 to resume its role as California's primary coastal highway. Throughout the rest of the Central Coast, US 101 switches between freeway and expressway status, but despite occasional cross-traffic it has unimpeded traffic, as there are no stop signs or traffic signals until San Francisco.
North of the US 101/SR 1 split, US 101 reaches Buellton, where it intersects with SR 246. North of Buellton, US 101 intersects SR 154 again, and in Los Alamos, it intersects SR 135. In Orcutt, US 101 and SR 166 run concurrently for until north of Santa Maria, where US 101 again intersects with SR 135. Vineyards surround US 101 in much of this area.
In San Luis Obispo County, US 101 passes through Nipomo, then intersects with SR 227 in Arroyo Grande. US 101 and SR 1 form another concurrency in Pismo Beach. Thereafter, the highway turns inland to San Luis Obispo, where US 101 reconnects with SR 227, and SR 1 splits off again. North of San Luis Obispo, US 101 ascends the Santa Lucia Range on a 7% incline via the Cuesta Grade, cresting at before descending north of the range. After the grade, US 101 has an interchange with SR 58 near Santa Margarita, and another with SR 41 in Atascadero. US 101 next passes through Templeton, and upon exiting, it runs concurrent with SR 46 for about until Paso Robles. US 101 continues north through San Miguel, where it enters Monterey County inside Camp Roberts.
North of Camp Roberts, US 101 passes the San Ardo Oil Field about south of San Ardo. Between San Lucas and King City, US 101 crosses the Salinas River three times and also intersects SR 198. US 101 then enters the Salinas Valley, known as America's Salad Bowl, where it travels through Greenfield, Soledad, Gonzales, Chualar, and Spence. US 101 then enters Salinas, where it has junctions with SR 68 and SR 183. North of Salinas, US 101 and SR 156 run concurrently for approximately . Within San Benito County, SR 156 splits off near San Juan Bautista, after which US 101 intersects with SR 129. US 101 also crosses the San Andreas Fault in this area. Map provided.
San Francisco Bay Area US 101 crosses the Pajaro River watershed into Santa Clara County, San Francisco Bay Area's southernmost county. US 101 then intersects SR 25, then continues north to Gilroy, where it changes from expressway to freeway. US 101 and SR 152 run concurrently for in this area; after which US 101 passes near San Martin and Morgan Hill in the Santa Clara Valley.
US 101's surroundings become increasingly urbanized as it approaches San Jose, where it intersects with SR 85. US 101 bypasses downtown San Jose to the east, passing through largely residential areas and also intersecting with I-280 and I-680 at the Joe Colla Interchange. US 101 then turns northwest as it continues through San Jose and intersects with I-880, then has a partial junction with SR 87. In Sunnyvale, US 101 intersects with SR 237 and SR 85, the latter for the second time. US 101 continues northwest through the South Bay, passing the Silicon Valley campuses of several major technology corporations, including IBM, Intel, Nvidia, and Google.