U.S. Route 101 in California

Route description

Running 808 mi through California, US 101 is defined in section 401 of the California Streets and Highways Code (SHC) simply as Route 101:

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. The American Association of State Highway and Transportation Officials (AASHTO)'s U.S. Route logs, along with most maps, have included the bridge as part of US 101, despite California's legal definition. The bridge along with the rest of US 101 is also part of the National Highway System, a network of highways that are considered essential to the country's economy, defense, and mobility by the Federal Highway Administration.

US 101 is part of the California Freeway and Expressway System, and portions of it are eligible to be included in the State Scenic Highway System. It is officially designated as a scenic highway by the California Department of Transportation (Caltrans) from Goleta to Las Cruces in Santa Barbara County, and through Del Norte Coast Redwoods State Park in Del Norte County. This designation means that there are substantial sections of highway passing through a "memorable landscape" with no "visual intrusions", where the potential designation has gained popular favor with the community.

Southern California

US 101 begins in Los Angeles at the East Los Angeles Interchange, a major freeway junction that includes I-5, I-10, and SR 60. This six-lane portion of the route is the northerly continuation of the Santa Ana Freeway, inheriting that title from I-5. After 2 mi, US 101 curves west and reaches the San Bernardino Split, a three-way junction with the San Bernardino Freeway that transitions into I-10 to the east. US 101 travels on a 1944 bridge over the Los Angeles River before passing the Los Angeles Union Station.

Proceeding in a generally northwestern direction, US 101 runs through downtown Los Angeles via the Downtown Slot beneath the northern edge of Los Angeles Civic Center, and encounters SR 110 at the Four Level Interchange. Starting here, US 101 is named the Hollywood Freeway. The route then passes through the L.A. neighborhoods and into Hollywood, sharing a short segment with SR 2 through the urban area. US 101 runs up the Santa Monica Mountains through Cahuenga Pass before descending into the San Fernando Valley. It passes right next to the Universal Studios Hollywood before reaching the Hollywood Split where it abruptly shifts westward, superseding SR 134 on the Ventura Freeway, while the Hollywood Freeway continues northward as SR 170.

From the interchange, US 101 is an east–west highway. Such geographical orientation of the Ventura Freeway and the north–south designation which appears on the freeway signs can be confusing to visitors. The same freeway entrance can often be signed as "101 North" and "101 West"; this is most common in the San Fernando Valley where the local east-west signing does not match the Caltrans' proper statewide north-south designation. US 101 meets with I-405 in Sherman Oaks, and with Topanga Canyon Boulevard (SR 27) in the Woodland Hills neighborhood. By Calabasas, US 101 undergoes a change of scenery to a somewhat rural character, from a heavily urbanized scene observed since its southern terminus, as it enters Canejo Valley, where it crosses the border of Los Angeles County into Ventura County. In Thousand Oaks, US 101 has an overlap with SR 23 for about 2.44 mi, until the three-way interchange with the Moorpark Freeway that SR 23 follows.

Continuing westward, US 101 climbs the Conejo Grade on a 7%-grade incline before descending into the Oxnard Plain, where it serves Camarillo and Oxnard. The coastside SR 1 runs concurrently on the freeway starting at Oxnard; there is no signage confirming the overlap despite maps depicting this. Upon crossing the Santa Clarita River, the two routes reach Ventura, where the freeway has an interchange with SR 126 and SR 33.

Central Coast

US 101 crosses the Ventura River that runs through the Emma Wood State Beach. It is at this point that the route comes within view of the Pacific Ocean for the first time on its journey. The route passes La Conchita before crossing into Santa Barbara County and encountering SR 150 that links Lake Casitas; at this point, the "Ventura Freeway" name ends, but US 101 continues as a freeway. In Santa Barbara, US 101 has a junction with SR 154. In Goleta, US 101 encounters SR 217 that connects to the University of Santa Barbara. Thereafter, US 101 narrows to four lanes, gradually tapering down from ten since Hollywood, and switches from freeway to expressway, albeit with several interchanges serving the beaches and parks along the Gaviota Coast. This rural stretch of highway often comes no more than 1 to from the shore. At Gaviota, US 101 sharply curves north, thus resuming its original north-south alignment, and heads inland across the Santa Ynez Mountains, where the northbound lanes pass through the Gaviota Tunnel (no tunnels exist on the southbound side).

Throughout the rest of the Central Coast, US 101 oscillates between freeway and expressway status, but has unimpeded traffic as there are no traffic signals until San Francisco.

A few miles north of the Gaviota Tunnel, SR 1 splits from US 101 and heads northwest into Lompoc to resume its role as the primary coastal highway. US 101 heads into Buellton, where it encounters SR 246. North of town, US 101 meets with SR 154 a second time, and SR 135 at Los Alamos. By Orcutt, US 101 picks up a 3 mi overlap with SR 166 until north of Santa Maria, where US 101 also reconnects with SR 135.

In San Luis Obispo County, US 101 encounters SR 227 at Arroyo Grande. The highway collects SR 1 in another overlap as it passes through the oceanfront town of Pismo Beach. With SR 1 still in tow, US 101 heads back inland into San Luis Obispo, where SR 227 loops back into the highway and SR 1 splits off for Big Sur. North of San Luis Obispo, US 101 ascends the Cuesta Grade on a steep 7% grade within the Santa Lucia Range, cresting at an elevation of 1522 ft. At the bottom of the mountain, the route encounters SR 58 that links to Santa Margarita, and is an important byway to Bakersfield and Barstow. US 101 then enters Atascadero, where it meet SR 41 that interconnects the town with Morro Bay and Fresno. Upon reaching Templeton, US 101 is joined by SR 46 for about 3 mi until Paso Robles, where it heads east serving as an alternate route to SR 41. After San Miguel, US 101 crosses into Monterey County while bisecting the Coast Guard post grounds of Camp Roberts.

US 101 bypasses the San Ardo Oil Field about 5 mi south of the proverbial location. Between San Lucas and King City, The highway crosses the river three times and encounters SR 198, which provides a critical link east to Hanford. US 101 travels through the Salinas Valley, known by the motto "America's Salad Bowl" for its agricultural significance. Heading northwestward, it cuts through small valley towns before reaching Salinas, where it encounters SR 68 that provides an important connection with Monterey, and SR 183 close to the city's center. North of Salinas, US 101 has an interchange with SR 156 at Prunedale that follows it for the next 8 mi approximately. Making a brief trek into San Benito County, US 101 arrives at SR 129, while at the same time, SR 156 splits off the highway on an interchange near San Juan Bautista. Within the same area, US 101 crosses the seismically-active San Andreas Fault.

San Francisco Bay Area

Entering the San Francisco Bay Area, US 101 crosses the Pajaro River into Santa Clara County and quickly arrives at an interchange with SR 25, which heads southeast into Hollister. As US 101 reaches Gilroy, it becomes a steady freeway for the South Bay. In town, SR 152 meets with US 101 and runs concurrently north for 1 mi before branching off west into the business district. US 101 remains on the east sides of San Martin and Morgan Hill as it runs through the Santa Clara Valley.

The surroundings become increasingly urbanized as US 101 reaches San Jose, the largest city in the Silicon Valley. The freeway arrives at the interchange of SR 85, the first Bay Area freeway encountered. The route stays east of Downtown San Jose, passing through largely residential areas and arrives at the Joe Colla Interchange, the meeting point for I-280 and I-680. Continuing its course, US 101 turns west-northwest through north San Jose and meets with I-880, which serves cities along the East Bay shoreline, and a partial interchange with SR 87. Upon entering Sunnyvale, the route encounters the two freeway junctions of SR 237 and SR 85, for the second time, by Moffett Field. Throughout its trek in the South Bay, US 101 passes by or near the campuses of major technology corporations, including IBM, Intel, Nvidia, and Google.

By Palo Alto, US 101 enters the San Francisco Peninsula. The freeway serves communities along the west edge of the San Francisco Bay, which is occasionally viewable from the roadway. At East Palo Alto, US 101 enters San Mateo County and meets with SR 84, which runs across the bay on the Dumbarton Bridge. US 101 passes through Redwood City, Belmont, and San Carlos, and in San Mateo the route encounters SR 92, another key bay crossing over the San Mateo Bridge. At San Bruno, US 101 passes the San Francisco International Airport, with direct ramp and flyover connections between the freeway and the terminals. It then arrives at I-380, which links with I-280 that has mostly avoided much of the urban areas. US 101 stays on the east side of South San Francisco. However, the scenery briefly yet abruptly changes to more natural as the freeway passes Brisbane on the east side of the San Bruno Mountain, running along a causeway separating the Brisbane Lagoon from the bay, before reaching Bayview Park, the location of the now-demolished Candlestick Park.

From San Francisco north, US 101 is a vital freeway thoroughfare for commuters in the North Bay. After crossing the Golden Gate Bridge, US 101 enters Marin County as the Redwood Highway. This leg of the freeway serves the urbanized eastern side of the county fronting San Pablo Bay. It climbs the Waldo Grade and passes through the Robin Williams Tunnel; afterward, it passes above the hillside town of Sausalito and descends to Richardson Bay, where SR 1 splits from the freeway and heads to the Pacific coast. Through Mill Valley, US 101 has a junction with the west end of SR 131 (Tiburon Boulevard) that provides a connection with Tiburon and a ferry service to Angel Island. US 101 passes through the twin towns of Corte Madera and Larkspur, running by the Larkspur Ferry Terminal. In San Rafael, US 101 encounters the partial junction of I-580 before running just east of the downtown area and the Marin County Civic Center. Farther north in Novato, the route encounters SR 37 that links to Vallejo, and runs alongside the Olompali State Historic Park on the northern outskirts. This outlying area that the freeway traverses is sparsely populated, as the voter-approved Novato–Petaluma Community Separator protects it against most development.

US 101 crosses into Sonoma County, where vineyard patches frequently dot the open spaces surrounding the freeway, indicating entry into Wine Country. In Petaluma, US 101 picks up a concurrency with SR 116 that extends into Cotati, where SR 116 splits off west to Sebastopol. US 101 continues northward through neighboring Rohnert Park, home of the Sonoma State University and the Graton Resort. At downtown Santa Rosa, it has a junction with SR 12 and passes over the Railroad Square on the Robert L. Bishop Memorial Bridge, an elevated span. Upon reaching Windsor, US 101 becomes more lightly traveled as the landscape gradually evolves into a more bucolic setting. The freeway crosses the Russian River in Healdsburg and then parallels the river up the Alexander Valley, where it avoids the winegrowing valley floor by grazing the west hills overlooking the valley. SR 128 joins US 101 at Geyserville, then leaves the freeway at Cloverdale. US 101 then ascends a steep hill just before leaving the Bay Area.

North Coast

US 101 is largely a two-lane road for much of the Redwood Empire, with occasional expressway and freeway spurts. The route crosses into Mendocino County, the first county in the Emerald Triangle, a region known for cannabis cultivation. Starting out as a freeway for about 1 mi into the county, US 101 crosses the Russian River again and quickly changes to an expressway before following the river along the pertinent canyon. The highway passes Frog Woman Rock, a massive rock feature central to local Pomo lore. Entering Sanel Valley, US 101 narrows to a two-lane road, the first time since leaving San Francisco, and crosses the river one final time. In Hopland, the road meets with SR 175 that heads east into Old Hopland.

US 101 widens into a four-lane freeway approaching Ukiah, and encounters SR 253 that connects Boonville, as well as Talmage Road (unsigned SR 222) that leads east to the City of Ten Thousand Buddhas. In the community of Calpella close to Lake Mendocino, SR 20 merges with US 101 for the next 15.5 mi to Willits. The combined routes ascend the 1956 ft Ridgewood Summit, the highest elevation for US 101's entire trek through California. Just south of Willits, SR 20 separates from US 101 and serves the town proper, as the main highway bypasses the town to the east.

US 101 intersects with SR 162, then reaches Laytonville inside Long Valley. After reaching Rattlesnake Summit (1796 ft), US 101 begins to follow the South Fork Eel River. By Leggett, US 101 meets SR 1 for the last time on an at-grade intersection. The highway makes a series of sharp curves to match the contours of the river into Piercy. This section of US 101 is also prone to frequent landslides. Caltrans shooflied the most difficult section in 2009 with unique construction of two bridges known collectively as the Confusion Hill Bridges. This project, funded by an emergency act from the state legislature, moved the highway across the Eel River away from the troubled spots to prevent disruption in commerce and travel from infrequent, but costly, winter closures on the main transportation route to the far North Coast. Between Cummings and Cooks Valley, US 101 is shadowed closely by two discontinuous sections of SR 271, which are the old alignment of the highway through the vicinity.

Cooks Valley marks the arrival in Humboldt County for US 101. The route bisects Richardson Grove State Park where, because of the narrow lanes and towering redwood trees, standard-sized trucks in compliance with the Surface Transportation Assistance Act (STAA) are prohibited through the park. North of the park boundary, many rural villages straddle US 101, and the highway travels along the eastern boundary of the 53000 acre Humboldt Redwoods State Park, California's third-largest state park and an ecological province containing the largest remaining old-growth redwood forest in the world. A preserved portion of the original, outmoded alignment, named the Avenue of the Giants (SR 254) for the huge, centuries-old redwood trees, parallels the main road for over 30 mi. US 101 passes next to the Pacific Lumber Company yard in Scotia and through nearby Rio Dell, crossing the Eel River multiple times.

Approaching Fortuna, US 101 crosses the Van Duzen River, and reaches the western terminus of SR 36. After Fortuna, US 101 runs through the Humboldt Bay National Wildlife Refuge and around Humboldt Hill through Fields Landing, before coming close to the Humboldt Bay Nuclear Power Plant. Entering Eureka, US 101 transitions onto a surface street complete with the first traffic lights since San Francisco. At downtown Eureka, the route cuts east along Humboldt Bay on a one-way couplet for 5 mi. At the northern city limit, US 101 crosses the tributary formed by the Eureka Slough and Freshwater Creek on an expressway alignment skimming the bay. US 101 becomes an unobstructed freeway south of the center of Arcata and passes the California State Polytechnic University, Humboldt campus. Proceeding north it passes the junction for SR 299 in the Valley West district of the college town.

US 101 continues north as it skirts past McKinleyville on a high bluff north of the Mad River. As the highway reaches Clam Beach, motorists get their first full view of the Pacific Ocean north of the Golden Gate. North of Trinidad, the route narrows to one lane in each direction after crossing Big Lagoon to pass inland of Stone Lagoon and follow the coastal bar between Freshwater Lagoon and the Pacific Ocean south of Orick. US 101 becomes a 14 mi undivided freeway through Redwood National and State Parks running inland east of the Prairie Creek Redwoods State Park boundary.

HOV lanes

High-occupancy vehicle (HOV) lanes are built sporadically along US 101 and require two or more persons (the driver and at least one passenger) for each vehicle to access. HOV restrictions are enforced on a part-time basis during the weekdays, so that they function as general-purpose lanes for solo drivers outside the restriction hours, which vary for each HOV segment. The HOV lanes in Marin and Sonoma counties are the second longest in California, with a contiguous length of about 52 mi in each direction from the Richardson Bay Bridge to Windsor. In San Francisco, the right-hand lanes on the Lombard Street segment of US 101 have been designated as temporary HOV lanes in a pilot project launched by the San Francisco Municipal Transportation Agency (SFMTA) in 2021.

Tolls

Express lanes

High-occupancy toll (HOT) lanes along US 101 between SR 237 in Mountain View and Whipple Avenue in Redwood City opened on February 11, 2022. These express lanes were extended to I-380 in San Bruno on March 3, 2023, and are planned to be extended further south to I-880 in San Jose in fall 2026.

, the HOT lanes' hours of operation are weekdays between 5:00 am and 8:00 pm; they are otherwise free and open to all vehicles at other times. Solo drivers are tolled using a congestion pricing system based on the real-time levels of traffic. Two-person carpools are charged 50 percent of the posted toll. Carpools with three or more people and motorcycles are not charged. All tolls are collected using an open road tolling system, and therefore there are no toll booths to receive cash. Each vehicle using the HOT lanes is required to carry a FasTrak Flex transponder with its switch set to indicate the number of the vehicle's occupants (1, 2, or 3+). Solo drivers may also use the FasTrak standard tag without the switch. Drivers without any FasTrak tag will be assessed a toll violation regardless of whether they qualified for free.

The segment of the express lanes in Santa Clara County is co-administered by the Santa Clara Valley Transportation Authority (VTA) while the segment in San Mateo County is co-administered by the separate San Mateo County Express Lanes Joint Powers Authority, and therefore drivers will see two separate toll charges if they cross the county line.

Golden Gate Bridge

Main article: Golden Gate Bridge#Tolls

Tolls are collected only for southbound traffic on the Golden Gate Bridge headed to San Francisco. All-electronic tolling is also used on the bridge, and can be paid by either a FasTrak transponder or license plate tolling. The high-occupancy vehicle (HOV) lane leading to the bridge requires a car with three or more people.

History

Juan Bautista de Anza National Historic Trail

The US 101 Highway is part of the auto tour route of the Juan Bautista de Anza National Historic Trail, a National Park Service unit in the United States National Historic Trail and National Millennium Trail programs. In 2005, Caltrans began posting signs on roads that overlap with the historic 1776 Juan Bautista de Anza trail route, so that California drivers can now follow the trail.

Historic route: San Diego to Los Angeles

Instead of terminating in Los Angeles, US 101 once continued all the way south through San Diego to the Mexico–United States border in San Ysidro. However, this part was decommissioned on July 1, 1964, in favor of I-5. Though much of U.S. Route 101 has been superseded by I-5, several street segments of former Route 101 exist.

Historic route in San Diego County

Much of the route in northern San Diego County is County Route S21; this includes Coast Highway in Oceanside, Carlsbad Boulevard in Carlsbad, Coast Highway 101 in Encinitas, Camino del Mar in Del Mar, and Torrey Pines Road in Torrey Pines. In San Diego, one alignment entered La Jolla Village on La Jolla Blvd, while a newer alignment went through Rose Canyon under what is now I-5. Roads followed by US-101 in San Diego included Mission Bay Drive, Pacific Hwy, Harbor Drive and Main Street. It ran along National City Blvd in National City, Broadway in Chula Vista and Beyer Blvd in San Ysidro.

Oceanside–Carlsbad freeway bypass

By the early 1950s, traffic had become very heavy on US 101 through Oceanside and Carlsbad. The US 101 freeway bypass (Oceanside-Carlsbad freeway bypass) was built in 1953 and completed in 1955 by the California Department of Public Works (now Caltrans) and brought up by the San Diego Highway Development Association on a US 80/US 101 discussion on how to resolve the huge traffic loads on US 101 in Oceanside. Today it is part of I-5 and Palomar Airport Road. It follows I-5 from Coast Highway (former Hill Street exit) in Oceanside to Palomar Airport Road in Carlsbad. From there the US 101 bypass went onto Palomar Airport Road to merge with US 101 Bus. on Carlsbad Boulevard. As it approached the Coast Highway/SR 76 exit on southbound I-5 in Oceanside, US 101 Bus. split off. US 101 Bus. followed the original US 101 through downtown Oceanside and Carlsbad as former Hill Street/Carlsbad Boulevard (CR S-21) while the US 101 freeway followed modern I-5 and Palomar Airport Road. The south end of the freeway bypass is Carlsbad Boulevard and Palomar Airport Road and the north end is I-5 and the Coast Highway/SR 76 exit. The south end was modified after US 101 was decommissioned between the East Los Angeles Interchange in Los Angeles and the Mexican border in San Ysidro. This freeway construction by the California Department of Public Works put US 101 on an all new highway route alignment to relieve Oceanside and Carlsbad of their very heavy bumper-to-bumper burdensome traffic problem. Also before the bypass in the 1950s, US 101 followed North Coast Highway (formerly Hill Street) from San Luis Rey Mission Expressway (SR 76 and north end of the Oceanside–Carlsbad freeway bypass) to Harbor Drive. From there it followed Harbor Drive to Vandergrift Boulevard, San Rafael Drive, and the freeway onramp for I-5 north near the Camp Pendleton north entrance guardhouse gate. It merges with the I-5 northbound onramp to shoot onto the southbound lanes of I-5 to follow the freeway lanes all the way to Las Pulgas Road in Camp Pendleton.

Historic route in Orange and Los Angeles Counties

An old orphaned alignment of US 101, that ran through the cities of Mission Viejo, Laguna Niguel, San Juan Capistrano, Dana Point, and San Clemente, was located in south Orange County. The old roadway, from a dead end just west of I-5 and east of the railroad tracks in Mission Viejo to Cristianitos Road in San Clemente, followed Camino Capistrano, Doheny Park Road, Coast Highway and El Camino Real. It had interchanges with I-5 and California State Route 1. It was replaced by the San Diego Freeway (which US 101 became part of in 1958) and finally replaced by I-5 in 1968.

In northern Orange County, US 101 followed Harbor Boulevard. U.S. Route 101 left Orange County, traversed southeast Los Angeles County, and entered the City of Los Angeles along Whittier Boulevard.

El Camino Real: Los Angeles to San Francisco

Significant portions of US 101 from its southern terminus to the San Francisco Bay Area is designated as the Royal Road or El Camino Real. The commemorative route connects the former Alta California's 21 missions.

A former route of the highway over the Gabilan Range on the San Juan Grade to San Juan Bautista was bypassed in a 1932 realignment. Instead, shortly after leaving Salinas, US 101 joins SR 156 in Prunedale for about 8 mi as it crosses the mountains further north, through the Prunedale Cutoff.

Before the Golden Gate Bridge was completed in 1937, there was regular vehicle ferry service across the Golden Gate strait, running from the Hyde Street Pier to Sausalito. Under the California Streets and Highways Code § 401, the Golden Gate Bridge is legally not part of US 101. The portion of US 101 starting from Los Angeles ends at "the approach to the Golden Gate Bridge" and then resumes at "a point in Marin County opposite San Francisco" to the Oregon state line. The bridge itself is maintained by the Golden Gate Bridge, Highway and Transportation District instead of Caltrans.

From the 1940s to 1991, various segments of US 101 between Los Angeles and San Francisco were upgraded to either a freeway or expressway. In the Los Angeles area, the first segment of the Hollywood Freeway through the Cahuenga Pass opened in 1940, while the segment from the San Fernando Valley to Downtown Los Angeles opened in 1954, replacing Cahuenga Boulevard. The Ventura Freeway then opened in 1960, replacing Ventura Boulevard. The segment of the original two-lane alignment between Emma Wood State Beach north to the Mobil Pier Undercrossing near Sea Cliff, which followed the historic Rincon Sea Level Road, was the re-signed as part of SR 1.

The last traffic signals along the route between the Los Angeles area and the San Francisco Bay Area were removed in 1991 when the section through downtown Santa Barbara was constructed to freeway standards after years of disagreement over the impact that the original elevated design would have on the community.

In the San Francisco Bay Area, US 101 was originally divided. US 101W followed the same general right-of-way of today's US 101 through the region, primarily along what was originally signed as Bayshore Boulevard. US 101E then generally followed the right-of-way taken by today's I-880 from San Jose to Oakland, then across the Carquinez Bridge to follow what is now SR 37, joining US 101W. The US 101E designation was removed by the 1940s and became SR 17 (later designated as I-880 and the westernmost section I-580), running from San Jose to Oakland and then across the Richmond–San Rafael Bridge. Meanwhile, Bayshore Boulevard was later redesignated as the US 101A bypass and then eventually upgraded to what is now the Bayshore Freeway. The first stretch that was completed between Redwood City and South San Francisco was the Bay Area's first freeway when it opened in 1947. After the entire Bayshore Freeway was completed in the early 1960s, the old alignment along the peninsula was renumbered and renamed as SR 82/El Camino Real.

Various other freeway or expressway bypasses along the California Central Coast were also built. In 1991, the last traffic signal along US 101 between Los Angeles and San Francisco was taken down in Santa Barbara. The primary control city that is listed on freeway signs along northbound US 101 through the Central Coast region remains San Francisco.

As the result of freeway revolts in San Francisco in the 1950s, a direct freeway connection through the city to the Golden Gate Bridge has never been built. The Central Freeway was completed to extend from the Bayshore Freeway to Turk Street in 1959, before the San Francisco Board of Supervisors voted to remove the remainder of the Central Freeway and most other proposed freeways from the city's highway plan. For decades, southbound traffic on US 101 flowed on the one-way Turk Street from Van Ness Avenue to the Central Freeway, while northbound traffic used the parallel Golden Gate Avenue. After the 1989 Loma Prieta earthquake damaged the structure, the segment of the Central Freeway north of Market Street was replaced with the surface-level Octavia Boulevard; traffic on US 101 was then eventually re-routed to exit south of that at Mission Street/South Van Ness Avenue. With no direct freeway along US 101 through the City of San Francisco, the old US 101E/I-880/I-580 route remains as a faster bypass through the Bay Area.

In the wake of the dot-com bubble expansion, the segment of US 101 between Morgan Hill and San Jose, also known as the Sig Sanchez Freeway, expanded to eight lanes between Cochrane Road and SR 85 exits between 2001 and 2003 and a new interchange at Bailey Avenue, which had been planned since the 1970s, opened in 2004. Originally, the 10 mile was only four lanes (it was planned to have six lanes when opened in 1984). The rebuilt segment was to alleviate the consistent congestion that had expanded as far south as Masten Avenue coming from Gilroy, and as far north as Bernal Road coming from San Jose. Traffic now typically only runs slow between the Bailey Avenue and East Dunne Avenue exits.

The interchange at the beginning of I-280 and I-680 in San Jose was constructed years before its completion. The three flyovers, with no on ramps or off ramps connecting them stood at 110 ft over US 101 for years in the 1970s (the SR 87/I-280 interchange also had this at the same time). It became the butt of many local jokes. The highlight prank occurred in January 1976, when a 1960 Chevrolet Impala was placed on the highest bridge overnight, where it obviously would be impossible to drive. The following day, San Jose City Councilman Joe Colla was photographed standing next to the car, a photo which was circulated across many newspapers. It has been suggested this stunt helped lead to funding to complete the freeway. In 2010, the interchange was named the Joe Colla Interchange.

Redwood Highway: Marin County to Del Norte County

The Redwood Highway opened from from Sausalito to Grants Pass, Oregon with the completion of the Douglas Memorial Bridge in 1926. It was named as "The Redwood Highway" by A.D. Lee, a Crescent City hotelier, inspired by the Save the Redwoods movement. The Redwood Highway Association marketed the beauty of the route through ancient forests on the mostly dirt and gravel road to boost tourism, most successfully with the internationally publicized 480-mile ultramarathon the Redwood Highway Marathon held in 1927 and 1928.

An abandoned segment of the Redwood Highway, US 101, located in the Redwood National and State Parks near Klamath was added to the National Register of Historic Places in 1979.

Freeway segments along the Redwood Highway portion of US 101 are not as prevalent as along the Los Angeles-San Francisco route. A notable segment of the old US 101 alignment is SR 254, also known as the Avenue of the Giants, in Humboldt Redwoods State Park. The freeway bypassing this scenic route, surrounded by towering Coast Redwoods, was completed in 1960. Several bridges along the segment of highway running along the Eel River were destroyed during the Christmas flood of 1964.

A freeway bypass of Cloverdale was constructed in the early 1990s, requiring the relocation of segments of the Northwestern Pacific Railroad. The new 4 mi roadway along with new frontages and relocated railroad were completed at a cost of $40 million ($ in adjusted for inflation). The highway opened over two weeks in March 1994. The old routing through town is on Cloverdale Boulevard.

Construction on a freeway segment bypassing Willits began in 2013. The bypass around Willits remained controversial because the intended route goes through protected wetlands. Construction was halted by US Army Corps of Engineers in June 2014 and work restarted the following month after Caltrans committed to extensive mitigation of the project. The 5.9 mi bypass around Willits opened to traffic in November 2016. The bypass included a 1.1 mi viaduct going over a flood plain. The freeway segment cost $459 million to complete ($ in adjusted for inflation), 50% more than what Caltrans first reported when it opened. Because the US 101/SR 20 intersection was originally inside Willits' city limits, SR 20 was then extended along the southern bypassed portion of former US 101. The northern bypassed portion of former US 101 in unincorporated Mendocino County has yet to be turned over to local maintenance, and therefore still exists within the state highway system under the unsigned designation of Route 101U (for "unrelinquished").

The city of Eureka has long resisted a freeway through it.

Future

The Wallis Annenberg Wildlife Crossing is a vegetated overpass spanning the Ventura Freeway and Agoura Road at Liberty Canyon in Agoura Hills. Once built, it will be one of the largest urban wildlife crossings in the United States, connecting the Simi Hills and the Santa Monica Mountains over a busy freeway with ten traffic lanes (including exit lanes).

The Richardson Grove section of US 101 has been proposed for a bypass for many years, but Caltrans conducted a study in 2000 which stated that a bypass was not cost effective and recommended realignment of US 101 within the redwood grove instead to accommodate modern-sized trucks in compliance with the Surface Transportation Assistance Act (STAA).

Names and memorials

US 101 bears various names and memorial designations throughout. Urban portions of the route in Southern California are named the Santa Ana Freeway, Hollywood Freeway, and Ventura Freeway at various points between East Los Angeles and Carpinteria, California. In 2008, the portion of US 101 that runs from the Conejo Grade to the Old Town district of Camarillo was dedicated as the Adolfo Camarillo Memorial Highway to honor the city's namesake and extends through the boundaries of the original Camarillo family ranch. In 2003, the portion of US 101 in Ventura County was named Screaming Eagles Highway in honor of the US Army 101st Airborne Division.

Portions of the route between Southern California and the Bay Area are named El Camino Real or El Camino Real Freeway, but such names are rarely used colloquially; the route number is used instead.

In the Bay Area, US 101 is called the South Valley Freeway, in reference to south Santa Clara Valley; the Bayshore Freeway, and Central Freeway. A portion of the route between Cochrane Road in Morgan Hill and SR 85 in San Jose is named the Sig Sanchez Freeway. The section of highway between SR 85 in Mountain View and Embarcadero Road in Palo Alto is officially known as the Frederick E. Terman Highway. In San Francisco, US 101 is called the James Lick Freeway, in honor of the philanthropist. The weaving stretch of the freeway on Potrero Hill is called the "Hospital Curve" due to the adjacent Zuckerburg San Francisco General Hospital. Surface street routings in the city are more commonly referred to by their street names rather than the route number.

From the North Bay onward, US 101 carries the Redwood Highway label and features several co-designations. The section from the Robin Williams Tunnel to I-580 in San Rafael is officially named the William T. Bagley Freeway, after the California assemblyman who often joked that it was the least congested for the area. The rural stretch of US 101 between Petaluma and Novato was ominously referred to as the "Novato Narrows" by locals, because of the reduction from six lanes to four and at-grade intersections. The name lost popular relevance after newly-added HOV lanes opened on September 29, 2025, culminating a 14-year highway overhaul project.

In Eureka, US 101 follows an artery called Broadway, though that name is largely unsigned and not registered on Caltrans' logs. The expressway portion of US 101 on the northern city limits is designated the Michael J. Burns Freeway, in honor of the state senator who was a proponent of California's highway system. US 101 splits onto a pair of one-way streets twice, in downtown Eureka and Crescent City: respectively, 5th and 4th Streets, M and L Streets.

Major intersections

(Southbound toll only; no state maintenance on bridge) southern end of Redwood Highway

Notes

References

References

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2. (November 11, 1926). "United States System of Highways Adopted for Uniform Marking by the American Association of State Highway Officials". [[United States Geological Survey]].
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9. {{CAFESystem
10. {{CA scenic
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13. {{Caltrans scenic info
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