U.S. Route 101 in California

Southern California

US 101 northbound as it enters downtown Los Angeles.

View northward from the Cahuenga Pass, 1972.

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 miles (3.2 km), 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.^[16]

Proceeding in a generally northwestern direction, US 101 runs through downtown Los Angeles via the Downtown Slot^[17] 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^[a] 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.^[16]

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.^[18] 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 Conejo Valley, where it crosses the border of Los Angeles County into Ventura County.^[19] In Thousand Oaks, US 101 has an overlap with SR 23 for about 2.44 miles (3.93 km), until the three-way interchange with the Moorpark Freeway that SR 23 follows.^[16]

Continuing westward, US 101 climbs the Conejo Grade on a 7%-grade incline^[20] 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.^[16]

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.^[16] Thereafter, US 101 narrows to four lanes, gradually tapering down from ten since Hollywood, and switches from freeway to expressway,^[b] albeit with several interchanges serving the beaches and parks along the Gaviota Coast.^[c] This rural stretch of highway often comes no more than one to two miles (1.6 to 3.2 km) from the shore.^[22][19] 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).^[16]

Throughout the rest of the Central Coast, US 101 switches intermittently between freeway and expressway status,^[19] but it has unimpeded traffic in spite of occasional cross-traffic, as there are no traffic signals until San Francisco.^[23]

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 three-mile (4.8 km) overlap with SR 166 until north of Santa Maria, where US 101 also reconnects with SR 135.^[16]

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.^[16] 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 1,522 feet (464 m).^[24] 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 three miles (4.8 km) 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.^[19][16]

US 101 bypasses the San Ardo Oil Field about five miles (8.0 km) 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.^[16] US 101 travels through the Salinas Valley, known by the motto "America's Salad Bowl" for its agricultural significance.^[25] Heading northwestward, it cuts through small valley towns^[d] 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 eight miles (13 km) 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.^[16] Within the same area, US 101 crosses the seismically-active San Andreas Fault.^[26]

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 one mile (1.6 km) 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.^[16]

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.^[19] 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.^[16]

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.^[16] 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,^[27] before reaching Bayview Park, the location of the now-demolished Candlestick Park.^[28][16]

US 101 enters the city and county of San Francisco and meets with I-280 again on the Alemany Maze.^[16] It reaches the western terminus of the San Francisco Skyway, which is signed as I-80 but not officially defined as such.^[29] US 101 turns west and follows the old Central Freeway viaduct near the city's Civic Center before suddenly transitioning northward on Van Ness Drive, the first time that US 101 is carried along a surface street, upon which bus lanes for MUNI run through the middle of the street. The alignment also passes behind the city hall. US 101 turns west on Lombard Street; this alignment serves as the boundary between the Marina District and Pacific Heights. After the Palace of Fine Arts, US 101 transitions onto the grade-separated Presidio Parkway through the namesake park. This divided roadway passes through two pairs of tunnels—Main Post Tunnels and Battery Tunnels^[30]—and curves northward just as SR 1 joins the route near Crissy Field. The shared highways cross the Golden Gate Bridge.^[16]

From San Francisco north, US 101 is a vital freeway thoroughfare for commuters in the North Bay.^[31] After crossing the Golden Gate Bridge, US 101 enters Marin County as the Redwood Highway.^[32] 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.^[16] This outlying area that the freeway traverses is sparsely populated, as the voter-approved Novato–Petaluma Community Separator protects it against most development.^[33]

US 101 crosses into Sonoma County,^[16] where vineyard patches frequently dot the open spaces surrounding the freeway, indicating entry into Wine Country.^[34] 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.^[32] 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.^[16]

North Coast

US 101 is primarily 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. About one mile (1.6 km) into the county, US 101 crosses the Russian River again and quickly changes to an expressway before following the river along the pertinent canyon.^[16] The highway passes Frog Woman Rock, a massive rock feature central to local Pomo lore.^[35] 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.^[19][16]

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 miles (24.9 km) to Willits.^[16] The combined routes ascend the 1,956-foot (596 m) Ridgewood Summit, the highest elevation for US 101's entire trek through California.^[36] 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.^[16]

US 101 intersects with SR 162, then reaches Laytonville inside Long Valley. After reaching Rattlesnake Summit (1,796 feet or 547 metres),^[36] 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, crossing the waterway on two spans through Confusion Hill.^[16] This section of US 101 is also prone to frequent landslides.^[37] 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.^[16]

Cooks Valley marks the arrival in Humboldt County for US 101.^[16] The route bisects Richardson Grove State Park where, because of the narrow lanes, absence of shoulders, and towering redwood trees, standard-sized trucks in compliance with the Surface Transportation Assistance Act of 1982 (STAA) are prohibited through the park.^[6][7] North of the park boundary, many rural villages straddle US 101,^[e] and the highway travels along the eastern boundary of the 53,000-acre (210 km²) 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 miles (48 km). US 101 passes next to the Pacific Lumber Company yard in Scotia^[38] and through nearby Rio Dell, crossing the Eel River multiple times.^[16]

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 miles (8.0 km). 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.^[19]

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-mile (23 km) undivided freeway through Redwood National and State Parks running inland east of the Prairie Creek Redwoods State Park boundary.^[19]

Now inside Del Norte County, US 101 crosses the Klamath River before reaching Klamath as a two-lane road.^[16] The original placement of the highway near giant coast redwoods led to increased awareness of the destruction of the redwoods after decades of extensive logging, which ultimately led to the establishment of Redwood National Park in 1968.^[39] Further north in Crescent City, US 101 once again separates into a one-way couplet for nine blocks. Exiting Crescent City, US 101 turns northeast and becomes a freeway for the last time in California, built slightly to the west of the original two-lane alignment, now called Parkway Drive. Just as the three-mile (4.8 km) freeway portion ends, US 101 intersects the southern terminus of US 199, which at this point inherits the "Redwood Highway" moniker and heads northeast linking Grants Pass, Oregon. US 101 continues northward on a two-lane road on the eastern outlying area of Fort Dick and crosses the Smith River before reaching the village named for the river. Motorists are treated with a view of the ocean once again as US 101 continues into Oregon by Pelican State Beach.^[16]

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.^[45][46] These express lanes were extended to I-380 in San Bruno on March 3, 2023,^[47] and are planned to be extended further south to I-880 in San Jose in fall 2026.^[48]

As of January 2026^[update], the HOT lanes' hours of operation are weekdays between 5:00 a.m. and 8:00 p.m.; 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.^[49][50]

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; therefore, drivers will see two separate toll charges if they cross the county line.^[49]

Golden Gate Bridge

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 HOV lane leading to the bridge requires a car with three or more people.^[51]

El Camino Real

Long before California entered statehood, the sixteenth-century Alta California had a loose-knit network of economically essential transportation paths deemed in the jurisprudence of the monarchy of Spain as caminos reales, or "royal roads".^[52] In the late eighteenth century, Gaspar de Portolá, under the stewardship of Junípero Serra, led groups of Spanish missionaries on two expeditionary runs along the roadways in the coastal regions, with missions, pueblos and presidios being established in his wake between San Diego and Monterey.^[53] Six years after Portolá made his last northerly run, Juan Bautista de Anza followed Portolá's trail starting at the present-day Los Angeles area on his own journey from Nuevo México to reach the Presidio of San Francisco on March 28, 1776.^[54] The 1908 travelogue by George Wharton James titled Through Ramona's Country describes the road that the expeditions traced out,^[55] and El Camino Real became synonymous with it.^[56]

Despite modest improvements made to El Camino Real in the mid-nineteenth century, it was still difficult for some stagecoaches and freight wagons to navigate.^[57] The movement to preserve and memorialize El Camino Real took off when Anna Pitcher of Pasadena presented her plan of restoring the route in 1902.^[58] Organizations and government agencies quickly signed on to the effort. Later that year, the California Federation of Women's Clubs adopted the project.^[59] In 1904, the Los Angeles Chamber of Commerce formed a convention in support of commemorating El Camino Real at the city, with Charles Lummis in attendance.^[60] A second convention was held in Santa Barbara and was attended by eighteen state delegates, including two appointed by Governor George Pardee.^[61][62] Starting in 1906, the first set of distinctive bells marking El Camino Real was erected along the roadway—over time, the number of bells varied as they were repeatedly destroyed, stolen, and then replaced.^[63][64] In 1915, the Automobile Club of Southern California produced a tourist map covering El Camino Real and the missions.^[65]

El Camino Real was part of the Pacific Highway, a chain of highways that existed until 1926.^[66] It was added to the California Historical Landmarks, reference number 784, in November 1963,^[67][68] and has been codified in California's SHC (under Section 635).^[69]

Redwood Highway

Until the end of the nineteenth century, almost all commerce on the Redwood Coast was done by sea, whereupon ships would dock at portside towns scattered along the Pacific coastline to transport passengers and deliver goods benefiting nearby settlements.^[71][72] Amid the backdrop of a sprawling automobile industry, there were calls for a reliable highway north of the Golden Gate, since it could take days to travel by motorcar across the particularly isolated regions of the northern coastal ranges.^[73] Redwood logging companies also wanted an easier way to transport their products south to the markets,^[74] under pressure from a soaring demand for redwood lumber, compounded especially by the gold rush and recovery efforts after the 1906 earthquake.^[75] In 1910, the California government passed the State Highway Bond Act authorizing funds for a statewide road system, but constructing the north–south highway was still years off.^[72][76]

Construction of the highway began in the fall of 1917 in Del Norte County.^[76] A.D. Lee, a Crescent City-based hotelier, proposed the name "Redwood Highway" in 1921, to honor the work by the Save the Redwoods League to preserve the native redwood forests.^[77] Local communities, as well as San Francisco, endorsed the suggested name for the new corridor,^[78] and it was ultimately written into the state's legal definition in 1957.^[79] In response to outcry about the harm that the Redwood Highway projects might have on the surrounding forests, the California Highway Commission^[g] set stringent limits on how many trees could be cleared from the right-of-way.^[76] Logs from trees that had been cut down were often used as guardrails and drainage control devices on the highway,^[80] and as material for building a 4,000-foot (1,200 m) trestle over Big Lagoon, at the time the largest native wood structure on the state highway system.^[81] A section of the Redwood Highway was constructed between 1918 and 1919 on the tidal wetlands bordering Humboldt Bay, out of sediments dredged out of the marsh.^[82] Landslides and washouts as a result of torrential storms repeatedly frustrated progress as the Redwood Highway corridor projects dragged on.^[83]

The overall construction of the original Redwood Highway alignment lasted roughly nine years total, and during this period the roadway opened segment by segment. The final piece of the Redwood Highway came about with the dedication of the Douglas Memorial Bridge on May 17, 1926, where California and Oregon governors Friend Richardson and Walter M. Pierce attended the ceremony along with nearly four thousand people,^[84] and the subsequent opening on October 29.^[85][86] Built at a cost of $400,000 (equivalent to $7.3 million in 2025),^[87] the Douglas Memorial Bridge replaced a cable ferry service on the Klamath River at Requa.^[88][76]

On September 3, 1925, a caravan driven by forty men dressed in "cavemen" outfits journeyed down the Redwood Highway from Grants Pass to attend a convention in Sausalito celebrating the highway's accomplishments.^[77] The Redwood Highway Association marketed the beauty of the route through the forests on the mostly dirt and gravel road to boost tourism,^[89][90] most successfully with the internationally publicized 480-mile (770 km) ultramarathon, the Redwood Highway Marathon, held in 1927 and 1928, up until the Great Depression.^[91][92] The first paved section of the Redwood Highway opened in Ukiah, where Jack London became the first person to ride the new fourteen-mile (23 km) stretch on his way to Crescent City.^[72] In the 1930s, the California Automobile Association marked the Redwood Highway with new federally-approved uniform signage.^[93] The completion of the Golden Gate Bridge in 1937 cemented the connection with the North Coast localities along the Redwood Highway from the San Francisco Bay Area.^[94][95]

Planning, numbering and signing

In a resolution submitted to the Secretary of Agriculture on October 30, 1925, the American Association of State Highway Officials (AASHO) announced its intent to establish US 101 in California.^[96] According to the draft outline, US 101 would start at the Mexican border at Tijuana and continue across the Oregon state line south of Brookings after 935 miles (1,505 km), occupying El Camino Real and most of the Redwood Highway (while leaving out the Crescent City–Grants Pass section for US 199), and lining up with State Legislative Routes (LNR) 2 and 1 that existed prior to 1964.^[97] It would be the westernmost route in AASHO's countrywide grid of U.S. highways crafted for the contingent states of the time.^[98] The numerical selection for US 101 proved problematic in that it ran afoul with AASHO's own conventions regarding triple-digit highways. However, because it was the only available odd number to be assigned for the highway west of US 99, the numeral "101" has been treated as having two digits instead of three: a "10" and a "1".^[99] The US 101 designation received its official approval on November 11, 1926, its routing in California mostly unchanged from the conceptual phase.^{[100][101][h]}

The first trailblazer signs for US 101 popped up on the San Diego–Los Angeles segment in January 1928. This was also the first section of the entire route in the West Coast to receive new signs. The Automobile Club of Southern California and California State Automobile Association were each contracted to erect signs in Southern and Northern California, respectively, during the summer months of that year.^[102]

Between 1929 and 1936, US 101 was signed as US 101W along the San Francisco Peninsula, following El Camino Real; and as US 101E along the East Bay up to Oakland, before overlapping with US 40 westward across the San Francisco Bay by means of a ferry connection. Both split route components rejoined at the Hyde Street Pier in San Francisco.^[103] Prior to the construction of the Golden Gate Bridge, ferries shuttled passengers following US 101 between the pier and Sausalito.^[104] In 1928, the National Automobile Club conducted a survey for another split route in the northern counties, with US 101E following Redwood Highway.^[105] That plan never came to fruition, and US 101 was routed as is on the Redwood Highway.^[106]

Historic segment

At its inception, US 101 made its way across the San Diego suburbs, on Beyer Boulevard in San Ysidro, Broadway in Chula Vista, and National City Boulevard in National City.^[107] From there, it took a somewhat erratic path through the city, coming a few blocks close to Balboa Park before cutting through downtown. The route turned north onto India Street before heading out of the area. By the 1940s, US 101 was truncated onto Harbor Drive to avoid the downtown hub and bring it closer to the San Diego Bay.^[108] North of Mission Bay, US 101 suddenly turned west through Pacific Beach, before turning back north on La Jolla Boulevard, within eyesight of the Pacific Ocean. It served the business areas of La Jolla before getting onto Torrey Pines Road. A newer alignment took US 101 onto Rose Canyon Road farther inland.^[109][110]

Continuing northward at Del Mar, US 101 was aligned on the Torrey Pines bypass built in 1933.^[111] It had replaced a dangerous highway predating the federal designation that was "tortuous, steep and narrow" with fifty curves, as described by engineer E. E. Wallace of the California Department of Public Works District 11. At its opening, it was dubbed the "Million Dollar Highway" for being completed for slightly more than $1 million (equivalent to $24.87 million in 2025).^[112] The original bridge span over the Surf Line was retrofitted in 2013,^[113] and the second at the Los Peñasquitos Creek estuary was replaced with a wider, more stylistic design.^[114]

US 101 proceeded along the coastline through Solana Beach, Encinitas, Carlsbad, and Oceanside.^[115][116] Each town along the route used to be separated by open land.^[117] After Camp Pendleton, it entered Orange County and passed through San Clemente and Dana Point, then veered inland into San Juan Capistrano, Laguna Niguel, and Mission Viejo. US 101 zigzagged through Irvine and Tustin.^[118] A concentrated section in the latter town once had up to ten fuel stations and a famous auto repair shop known as the Tustin Garage for motorists traveling from the south.^[119] US 101 then followed Katella Avenue and Spadra Road, since renamed to Anaheim Boulevard and Harbor Boulevard, respectively.^[120] The route traversed southeastern Los Angeles County on Montebello Boulevard, then entered Los Angeles along Whittier Boulevard.^[121]

At Doheny Park north of San Clemente, US 101 split into two routes, with the main route heading northeastward, and US 101 Alternate serving the beachside cities before encircling the Santa Monica Mountains via Malibu and converging with the main route in Oxnard.^[122] In 1963, US 101 Alternative was re-designated as SR 1.^[123]

By the 1940s, as traffic on the Carlsbad–Oceanside corridor became increasingly heavy, it became clear that a new freeway bypass was necessary.^[124] After years of planning, field surveys, and debates over several proposed build alternatives, construction of the Oceanside–Carlsbad Freeway commenced in 1950, and the freeway opened to traffic on November 16, 1953, with a price tag of about $9.2 million (equivalent to $110.7 million in 2025), and paid for through a quarter-cent gas tax fund.^[125] This would be the first section of the San Diego Freeway to be put into service in San Diego County.^[126] The freeway grew in subsequent construction stages throughout the county, and by 1968 it was integrated with the Santa Ana Freeway, forming a seamless link into Orange County and beyond.^[127][128] US 101 was rolled over to the freeway with each completed segment,^[129] starting with the Montgomery Freeway completed in the 1950s.^[109]

In September 1963, California legislatures passed Collier SB 64 that streamlined numbered routes across the state.^[130] The bill, which became law in July 1964, also stipulated that U.S. highways would be removed in favor of Interstate highways. While many U.S. highways in California were phased out, US 101 is the longest of seven to survive.^[131][132] Nonetheless, by 1968, US 101 was eliminated on the Mexico–Los Angeles section and supplanted by I-5.^[109] As a result, about 135 miles (217 km) of length were trimmed off the route, and the southern terminus was shifted to its current location in Los Angeles.^[133]

Much of the surface roads on the old US 101 were relinquished for municipal and county control. Historic US 101 signs and markers have been set up along the original right-of-way branches.^[134] A majority of the historic route in northern San Diego County has received the designation of County Route S21.^[116] The section in Camp Pendleton has been closed off to the public.^[109] The 101 Café in Oceanside hosted events and exhibits dedicated to the route's history.^[126][135]

Modern developments

Los Angeles to San Francisco

The Downtown Slot, a subsurface leg of US 101 in downtown Los Angeles, first opened in 1954.^[136][101]

In 1924, Los Angeles voters backed the Major Traffic Street Plan that incorporated proposals for the Hollywood Freeway to address the city's worsening traffic congestion.^[137] Further, the Collier–Burns Highways Act of 1947 provided necessary cash infusions supporting the package.^[138] US 101 on the Hollywood Freeway through Cahuenga Pass opened in December 1940, for the first unit of construction. Many residential and commercial properties were acquired to make room for the new freeway, including a home once owned by Rudolph Valentino.^[139] A ten-mile (16 km) extension, from Vineland Avenue in the San Fernando Valley to Spring Street in the Civic Center district, opened on April 15, 1954, thus replacing Cahuenga Boulevard.^[140] In 2024, a beautification project was undertaken on 8.7 miles (14.0 km) of US 101 to emphasize the movie culture, with a 22-foot (6.7 m) steel art sculpture depicting fluttering filmstrips installed on the median in East Hollywood.^[141]

US 101 was transferred from Ventura Boulevard to the Ventura Freeway, which was fully completed in 1960;^[142] by then, it was called the Calabasas Freeway.^[143] US 101 was converted from expressway to full freeway through the Santa Barbara County line.^[144] The new alignment on the Conejo Grade replaced a curvy two-lane road built in 1914.^[145] The grade separation project in Camarillo, completed on March 24, 1954, eliminated the last railroad crossing for US 101 between Los Angeles and San Francisco.^[146] In April 2024, construction got underway of the Wallis Annenberg Wildlife Crossing, a vegetated overpass spanning the Ventura Freeway and Agoura Road at Liberty Canyon in Agoura Hills connecting the Simi Hills and the Santa Monica Mountains across ten travel lanes (including exit lanes). Upon completion, it would be the largest urban wildlife crossings in the world.^[147]

The roadway that would eventually become US 101 replaced the outmoded Rincon Sea Level Road in 1924;^[148] the segment of the original two-lane alignment from Emma Wood State Beach north to the Mobil Pier Road undercrossing near Sea Cliff was later re-signed as part of SR 1.^[149] By late 1961, US 101 was developed into a divided multi-lane corridor in Santa Barbara.^[150] Additionally, in November 1991, the last traffic signal along the highway between Los Angeles and San Francisco was taken down, culminating years of disagreement over how the original elevated design might impact the community.^[151] A four-phase project to add HOV lanes between Mussel Shoals and Santa Barbara was launched in 2008.^[152]

US 101 was upgraded to expressway standards through the Gaviota Gorge by September 1954, providing a respite for motorists from steep grades for which the original two-lane road was notorious.^[153] The Gaviota Tunnel opened to northbound traffic in fall 1953;^[154] the old road was repurposed for southbound traffic.^[155] At Las Cruces, north of the gorge, the construction of the interchange with US 101 and SR 1 in 1967, led to the demolition of a village store originally built in 1917.^[156]

The freeway and expressway alignments of US 101 bypassed many communities and town centers in the Central Coast counties in the mid-twentieth century.^[157] After 1959, the state government assumed maintenance of the El Camino Real bell markers while US 101 continued to be realigned onto the modern highway.^[158] A study showed in 1951 that frontage-road businesses along the new Santa Barbara–Buellton alignment saw minimal adverse impact on customer volume after it opened to traffic.^[159] This, combined with improvements into Santa Ynez Valley, lengthened US 101 by twelve miles (19 km), but shortened the travel time over this distance because of higher speed limits and lighter curves.^[160] Shortly after the 1938 opening of the expressway on Cuesta Pass, mail bandit Roy Gardner was injured after colliding with a truck on the road there.^[161][162] Additional lanes were created on the pass in 2004, complete with new truck pullouts.^[24] US 101 was built as a freeway for ten miles (16 km) in Salinas by 1954,^[163] and was incremented much later with the new Sala Road interchange.^[164] US 101 was constructed on the Prunedale Cutoff in 1932, diverting traffic away from the more hazardous road over Gabilan Range via the San Juan Grade.^[165] The maneuver shifted US 101 about three miles (4.8 km) west of San Juan Bautista.^[166] Three more interchanges were added during the 2014 road safety improvement operation.^[164] US 101 was constructed on the new four-lane alignment at Sargent in the early 1940s, moving it off the nearby winding roadway across the Pajaro River,^[167] and onto the freeway bypass through southern Santa Clara Valley by the 1960s.^[168]

In 1936, US 101 on the San Francisco Peninsula was truncated to the Bayshore Highway, which had finished in October 1929,^[169] and El Camino Real was re-signed as US 101 Alternate.^[170] However, in light of outrage from businesses over the changes, US 101 was reverted to El Camino Real in 1938, while US 101 Bypass was given to the Bayshore Highway.^[171] The first opened section of the Bayshore Highway was a tolled arterial starting on the present-day San Mateo Avenue in San Bruno, with the 7 Mile House tollbooth stationed in the Visitacion Valley district.^[172] Because physical median separations were lacking, deadly head-on collisions were a very common occurrence on the highway, hence lending it the nickname "Bloody Bayshore".^[169] In response to the accidents, coupled with a 101% increase in traffic volumes in the 1928–1939 duration, drawings for the proposed Bayshore Freeway were publicized and submitted on July 26, 1940.^[173] For the first unit of the project, the two-mile (3.2 km) San Mateo–Burlingame stretch was completed in mid-1947,^[174] representing the Bay Area's first freeway in service.^[175] Residents criticized fences installed to keep pedestrians out of traffic.^[174] The Bayshore Freeway between San Jose and San Francisco was fully ready for commuters by February 2, 1962.^[176] The freeway was designated as part of US 101, while El Camino Real was re-signed as SR 82.^[177] Construction of the Joe Colla Interchange wrapped up in 1981, after a budget shortfall froze progress in the 1970s.^[178] It was named after Joe Colla, the San Jose councilman who staged a widely-circulated photoshoot of himself standing by a 1960 Chevrolet Impala on an inaccessible ramp, as a means of helping secure funding for the interchange.^[179] In the wake of the dot-com bubble, the San Jose–Morgan Hill segment of US 101 was 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.^[180] Expansion to six lanes was proposed in 1984 for the ten-mile segment (16 km).^[181] The rebuilt segment has been designed to alleviate the consistent congestion that had stretched over a broad swath between Gilroy and San Jose.^[182][183] HOV lanes were added in San Mateo and Santa Clara counties under sales tax funds approved in a 1984 ballot measure;^[184] they were extended into southern San Jose and then into Morgan Hill over the next fifteen years.^[185][186] By 2023, the HOV lanes were converted to HOT lanes with use of electronic toll collection for the Mountain View–San Bruno section.^[187][188]

In San Francisco, plans were in place to build a direct connection to the Golden Gate Bridge on the Central Freeway, which would have served as a northerly continuation of the Bayshore Freeway.^[189] Heated backlash against new freeways by residents soon caught up to the project,^[190] so 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.^[191][192] Consequently, only a section of US 101 was completed up to Turk Street in 1959, before construction activity came to an effective halt.^[193] The 1989 Loma Prieta earthquake caused severe damage to the Central Freeway, prompting immediate closure for fear of structural instability.^[194][195] In 1998, residents voted to have the damaged viaduct dismantled, overturning a 1997 vote wherein a narrow majority wanted it rebuilt.^[196] In 1999, voters once again affirmed this by supporting Proposition I to press ahead with the freeway tearout, simultaneously defeating rivaling Proposition J that would revive the rebuild.^[197][198] Demolition was completed by 2005, and the vacated right-of-way was relinquished to the city to be redeveloped into Octavia Boulevard.^{[199][200][i]} In 2022, the San Francisco Municipal Railway (MUNI) built center bus lanes and landscaped medians on Van Ness Avenue as part of the Van Ness Bus Rapid Transit project, which took six years to complete.^[202] In 2009, the project began to replace Doyle Drive, which had been built in tandem with the Golden Gate Bridge in 1937, and was determined to be structurally deficient. The new Presidio Parkway opened to traffic in 2015, and incorporated two sets of tunnels designed to "heal the landscape" inside the Presidio.^[203] The Presidio Tunnel Tops recreational area, positioned above the tunnels, opened to the public in 2022.^[204]

Marin–Sonoma vicinity

Leading up to the 1960s, a bulk of improvements on US 101 in the North Bay centered on upgrading it from expressway to full freeway configuration, as well as bypassing cities.^[205][206] As a noted exception, state highway planners recommended that US 101 run through the heart of Santa Rosa instead of around it, bowing to successful lobbying efforts from downtown businesses.^[207] Completion of the Steele Lane interchange brought the highway to full freeway standards in Santa Rosa by summer 1965.^[208] In Marin County, the Sausalito–San Rafael section of US 101 was completed in the early 1930s, concluding with the one-quarter-mile (0.40 km) bridge made of redwood over Richardson Bay—a portion of this six- to eight-lane alignment in Corte Madera was also laid down on a plot of marshland.^[209][210] In 1935, Marin County supervisors enacted an ordinance banning billboards along US 101.^[209] The twin bores of the Robin Williams Tunnel^[j] opened individually in 1937 and 1954.^[211][212] The Richardson Bay Bridge was replaced with the current concrete span in 1956.^[213] Additional bypasses were constructed at downtown Novato and Geyserville in the 1970s.^[214][215] The four-mile-long (6.4 km) freeway bypass in Cloverdale was completed in March 1994, at a cost of $40 million ($86.9 million in 2025 adjusted for inflation), which included new frontages and relocated Northwestern Pacific Railroad trackage.^[216] The segment between Novato and Petaluma was upgraded to freeway specifications by 2019; the scope of the project involved two modified interchanges and a raised bridge over San Antonio Creek on the county line.^[217][218]

With an objective of addressing growing traffic needs, Caltrans and the Metropolitan Transportation Commission (MTC) unveiled a joint plan in 2000 that included, among other priorities, building continuous HOV lanes on US 101 in the North Bay counties;^[219] Caltrans reiterated this desire on the Comprehensive Multimodal Corridor Plan released in 2023.^[31] HOV facilities were already existent in Marin County, having been converted from contraflow bus lanes in the 1980s,^[220] but a persistent gap at San Rafael would not be filled until 2011.^[221] The final stretch of HOV lanes in Sonoma County opened to traffic in Petaluma in 2022, finishing the system in the county after two decades.^[222][223] The HOV lanes on the Novato–Petaluma stretch debuted on September 29, 2025, creating a unified facility between the two counties.^[218][224] Around that time, Caltrans updated the restriction hours for the carpool lanes to be consistent for both counties, whereas beforehand each county had different preferential hours.^[225] The altered schedule amounted to a total of nine hours per weekday, starting at 5:00 a.m. and ending at 7:00 p.m.^[226] Caltrans quickly received complaints from drivers saying that the extended HOV hours have led to confusion and increased travel times on US 101;^[227] as such, an online petition was launched urging the agency to reverse the HOV schedule, gathering more than 8,600 signatures as of November 2025^[update].^[228] Thus, Caltrans posted newer hours that shrank the HOV timeframe by 21⁄2 hours.^[226][229]

Redwood Empire

Freeway and expressway segments are not as prevalent for US 101 in the Redwood Empire as elsewhere in California.^[230] A variety of factors contributing to the fact came into play in the middle of the twentieth century. Business and tourist resort owners, who relied on people using the Redwood Highway for profit, voiced collective opposition to any bypasses within their areas.^[231][232] Likewise, there was controversy surrounding the context of "bypass".^[233] Conservationists campaigning to protect redwood growths from destruction pushed for the scenic and natural value of the environment, which they believed would be diminished with the development of a multi-lane highway. Roadway engineers also faced grueling challenges with treacherous terrain and staggering costs associated with redesigning US 101.^[234] Meanwhile, the Eureka-based newspaper, Times, expressed ardent support for a safer highway in its November 1951 issue, arguing that US 101 carried more vehicles than US 99. Many local economies and taxpayer groups echoed this sentiment. The Redwood Empire Association urged the State Highway Commission to not truncate the route outside state park boundaries.^[235] In 1955, California Assemblyman Frank Belotti introduced legislation that would allot $10 million (equivalent to $120.19 million in 2025) of the California State Parks' funds, collected from oil royalties, for the construction of a 23-mile (37 km) bypass through the Humboldt Redwoods State Park. Although Governor Goodwin Knight vetoed the bill, highway officials discussed other options at a district meeting in Garberville on February 8, 1956, where a compromise was eventually agreed upon to expand the proposed bypass to about 44 miles (71 km), while removing about 400 trees with heights not exceeding six feet (1.8 m) in earnest. The estimated cost was $36 million (equivalent to $426.32 million in 2025).^[236] A study showed that travel time on US 101 between San Francisco and Eureka was six hours in 1963, a reduction from eight in the prior decade.^[237]

In a first for the Redwood Highway in Mendocino County, US 101 on the Ridgewood Grade was widened to a four-lane expressway on October 31, 1954.^[238] The 14+1⁄2-mile (23.3 km) freeway in Ukiah was completed on November 8, 1965, in a project that lasted three years,^[239] and was extended north through Redwood Valley in the late 1980s.^[240] A freeway had been adopted for US 101 east of Hopland in 1964, but it was never constructed.^[241] In spring 2026, Caltrans began applying accessibility improvements to the surface highway through town, in accordance to the American Disabilities Act (ADA).^[242][243]

A six-mile (9.7 km) freeway bypass at Willits opened in November 2016, more than sixty years after it was initially proposed.^[244] The project, which broke ground in 2013, remained controversial even during execution, because the intended route took it through protected wetlands.^[245] Construction was halted by US Army Corps of Engineers in June 2014, but was restarted the following month after Caltrans committed to extensive mitigation of the project.^[246][247] The bypass included a 1.1-mile (1.8 km) viaduct across a flood plain.^[248] The freeway segment cost $459 million to complete ($616 million in 2025 adjusted for inflation), 50% higher than what Caltrans first reported when it opened.^[87][249] As a result of the bypass, the US 101/SR 20 junction that was originally inside Willits' city limits was moved to the new interchange south of town, from which SR 20 then followed the southern portion of the former US 101 before heading west. The remainder of the old route on the north side has yet to be ceded for local maintenance, and therefore still exists within the state highway system under the hidden designation of Route 101U (for "unrelinquished").^[250]

In remote rural areas of Mendocino, Humboldt and Del Norte counties, US 101 was redeveloped with enhanced grades and curve corrections in mind. A report by the State Highway Engineer had found that sight distance on much of the route was constricted to 1,600 feet (490 m).^[234] Work on the Outlet Creek–Reeves Creek leg north of Willits in the late 1930s eliminated forty-seven tight turns that the previous 1917 alignment had.^[251] The new alignment at Piercy replaced the one with a total curvature of 2,978 degrees, as opposed to 807 degrees on the improved road.^[252] North of Laytonville, US 101 was realigned at Sapp Creek by November 1937, in a $177,000 contract (equivalent to $3.96 million in 2025).^[253] In 2009, Caltrans shooflied a particularly difficult section north of Leggett with 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 disruptions caused by infrequent but expensive winter closures on the mainline.^[37][254]

The US 101 freeway bypass around Humboldt Redwoods State Park, surrounded by towering Coast Redwoods, was completed in the 1960s. The old two-lane alignment, better known as the Avenue of the Giants, became SR 254.^[255] The freeway bridge at Eagle Point, completed in 1964 at a cost of $1,028,000 (equivalent to $10.67 million in 2025), was considered innovative at the time for how and where it was constructed: it straddles a promontory, featuring eleven spans of 110 feet (34 m) mounted 100 feet (30 m) above the Eel River, with a specialized retaining wall carved into the overhanging sidehill midway on the bridge.^[256] Another freeway section from Hydesville to just south of Eureka was completed with bypasses at Fortuna and Loleta by the early 1960s,^[257][258] and augmented with the Herrick Avenue interchange in 1984, and the SR 36 grade separation in 2010.^[259] North of Eureka, the Arcata–Trinidad freeway was finished during the same early period.^[260] Plans to re-route US 101 around downtown Eureka have remained stalled due to enduring local opposition.^[261] The Big Lagoon trestle was demolished in favor of embankments for carrying the three-mile (4.8 km) expressway, which debuted on June 25, 1959, with a $1,835,000 commission (equivalent to $20.27 million in 2025).^[262]

US 101 was truncated onto the new alignment through Prairie Creek Redwoods State Park from the late 1980s to early 1990s.^[259] The original highway segment north of Berry Glenn is named Newton B. Drury Scenic Parkway, in honor of the fourth director of the National Park Service and executive director of the Save the Redwoods League.^[39][263] Incidentally, Drury was an influential figure in terms of US 101, in that, during his tenure as Chief of the Division of Beaches and Parks, he shared an op-ed containing a three-point summary on the highway commission's commitment to adopt bypass routes with minimized footprints through the forested parks.^[264] An abandoned 1920s segment of the Redwood Highway on the Del Norte County side of the Redwood National and State Parks was added to the National Register of Historic Places in December 1979.^[70]

Many sections of US 101 sustained damaged in the Christmas flood of 1964, with several bridges rendered unsafe for vehicles from fast-moving floodwaters.^[265][266] Repairs on the highway stretched well into the next year, concluding with the opening of a new bridge over the Klamath River on March 15, 1965.^[267] It replaced the Douglas Memorial Bridge that collapsed when floating debris carried by the raging current overwhelmed its support system. The remnant of the bridge on the south bank has been turned into a static monument and overlook platform accessible by foot.^[268][269]

Juan Bautista de Anza National Historic Trail

Parts of the US 101 corridor from Los Angeles to San Francisco coincide with the Juan Bautista de Anza National Historic Trail, a National Park Service unit in the United States National Historic Trail and National Millennium Trail auto tour programs.^[285][286]