Historical naming The portion of this highway from Los Angeles to San Diego was also co-signed as US 101 until 1964–1968. The portion of this highway from Woodland to Red Bluff roughly follows old US 99W. In California, the former western branch of Interstate 5 (the northern end of the spur into the Bay Area) connecting I-80 out of Vacaville to near Dunnigan, previously known as
I-5W, was renamed
I-505. Interstate 580 running between I-5 and I-80 was also once designated 5W; what is now I-5 (the stretch that runs through Sacramento) had been originally designated
I-5E. The term "Golden State Highway" was the popular name for US 99 through the length of California; the name was chosen in a public contest in 1927, but was never officially adopted. Since the construction of I-5, it has taken over the term "Golden State Freeway" from 99 south of the latter's southern terminus in Kern County.
Los Angeles area The Golden State Freeway was proposed by the
California Highway Commission in 1953. The proposal drew strong criticism from East Los Angeles residents as it would dissect and eliminate large residential and commercial areas of
Boyle Heights and Hollenbeck Heights. The proposal also seemed to indicate a disregard for the ethnic
Mexican American population of metropolitan Los Angeles. The "Boyle–Hollenbeck Anti–Golden State Freeway Committee" was formed for the purpose of blocking or rerouting the freeway. Then–
Los Angeles City Council member
Edward R. Roybal chaired that committee. After a five-day standoff with police, the home was seized and later demolished. The section between Orange County and Los Angeles was originally designed to have three lanes in each direction. Due to high traffic demand, the freeway underwent major extensions and widening in Orange County during the 1990s. Work from SR 91 north through the Los Angeles–Orange County line was then completed in 2010, and reconstruction between the county line and Interstate 605 was completed in 2023.
Newhall Pass The original route went through the towns of
Saugus and
Newhall, and then crossed Newhall Pass (current route of SR 14, the Antelope Valley Freeway). In 1862,
Beale's Cut was made in the construction of a toll wagon road. The by "slot" was dug with picks and shovels. That road would become part of the Midway Route. At the turn of the century, it was the most direct automobile route between Los Angeles and the San Joaquin Valley via the
Mojave Desert and
Tehachapi Pass.
Ridge Route The
Ridge Route refers to the section of highway between Castaic and Grapevine, through the Tejon Pass. The highway had its origins in the early 1910s, when a route was needed to connect Los Angeles to the Central Valley. Some believed that the only option was the route through the Mojave Desert and the Tehachapi Mountains, but a new route was discovered through the Tejon Pass. This route became known as the Ridge Route and saw almost constant planning, construction, and improvement from 1914 to 1970. The first road was completed in 1915. It was a slow, winding, two-lane road through the mountains with a speed limit of in some places. However, the need for improvements was realized soon after it was completed. The road was paved after
World War I, and several blind turns were opened up ("daylighted"). Even with these improvements in the 1920s, it became clear that a new route was needed to keep up with increasing demand. The Golden State Highway route would serve many farming communities across the San Joaquin Valley, but the West Side Freeway proposal would bypass all the Central Valley communities and thus provide a faster and more direct north–south route through the state and so was eventually chosen. Construction began in the early 1960s. There were just three phases for the . The first phase, completed in 1967, ran from the San Joaquin County line to Los Banos. The second phase, completed in 1972, extended the freeway south to Wheeler Ridge and connected it to SR 99. The freeway then started to see traffic, as in Stockton there were only between the West Side Freeway and the Golden State Highway. The third phase, completed in 1979, extended the freeway to Sacramento and connected it to the northern I-5. When the second phase of the freeway opened in 1972, it was a long and lonely route with no businesses alongside. Services were not easily available as the nearest towns were miles away and generally out of sight. It was common for cars to run out of fuel. Over time the West Side Freeway (I-5) saw the development of businesses serving the needs of travelers. For years, there has still been interest in designating the Golden State Highway route as its own interstate,
I-7 or I-9. The median on I-5 between Wheeler Ridge and Tracy is wide enough to accommodate widening the West Side Freeway to six or eight lanes, should the need arise.
I-5W and the San Francisco Bay Area I-5's more direct Los Angeles-to-Sacramento route bypasses San Francisco,
San Jose,
Oakland, and the rest of the San Francisco Bay Area. Original plans also called for a loop Interstate with a directional suffix, I-5W. Due to record levels of rainfall in 1980 the Boat Section was flooded with of water. Caltrans began constructing this section during the 1960s and 1970s. The freeway was engineered below grade so it would be out of the view of offices and shops in downtown Sacramento. To achieve this, the site was excavated and the seeping water was pumped from the area. An intricate drainage system, water pump and retaining wall are used to protect the freeway from the Sacramento River. However, the system slowly clogged up over the years with sand and silt buildup. Major repair work of the Boat Section began on May 30, 2008.
HOV lane expansion in Southern California I-5 through north San Diego County is currently undergoing expansion as part of the
North Coast Corridor project. The carpool lane expansion from Lomas Santa Fe Drive to SR 78 fully opened by late 2023. As part of this expansion, the bridge carrying I-5 over San Elijo Lagoon was replaced with a much wider bridge. Previously in 2007, a carpool lane opened between Lomas Santa Fe Drive and I-805, with a continuation of the lanes on I-805 to Governor Drive opening in 2016. There are plans to construct the last three miles from SR 78 to Oceanside Harbor Drive, however, there is a lack of funding for them, and there are no plans to set aside funding from the state to construct them. In Orange County, the HOV lane opened in the mid-1990s between SR 1 and SR 91, following the widening of the freeway between SR 55 and SR 91, between SR 91 and Artesia Boulevard in 2010, and between SR 1 and Avenida Pico in 2018. Multiple carpool flyovers were constructed during this time to connect motorists from one freeway's carpool lanes to the next (see Exit List for a list of them). In 2011, ground broke on a major expansion of the freeway through La Mirada and Norwalk in neighboring Los Angeles County to the I-605 interchange, which included a carpool lane to Florence Avenue. The carpool lane fully opened in 2022. Currently, in San Clemente, there are studies to extend the carpool lanes from their current terminus at Avenida Pico to Cristianitos Road at the county line. At an OCTA board meeting in August 2024, it was discussed that preliminary engineering is ongoing and will be complete next year. However, a timeline for actual construction was not provided. This extension would give way for I-5 to have carpool lanes for its entire length in Orange County, plus the newly widened section in Los Angeles County, for a total of 50 miles. OCTA and Caltrans are expected to work with the residents of San Clemente during the process, as several bridges may have to be replaced with wider ones, and buildings may have to be demolished for the widening. North of downtown Los Angeles, the freeway is currently going widening, which includes the addition of HOV lanes in four phases. The first phase was the opening of a carpool lane between carpool lane between SR 170 and SR 14 in 2011. A flyover between the carpool lanes of SR 14 and I-5 opened in 2014. The second phase was between
Buena Vista Street and SR 170, and the carpool lane opened in 2014. This phase also included a flyover between the existing carpool lane of SR 170 and the newly constructed I-5. The freeway in this phase went through no improvements, and used existing median shoulders to construct the HOV lane, thus all the original overpasses were retained, and some undercrossings also have no right hand shoulder as a result. A third phase saw the widening between SR 134 and Buena Vista Street, and the carpool lane opened in 2022. This phase gave room for the replacement of the Burbank Boulevard bridge, and the opening of a new interchange at Empire Avenue, which replaced the Scott Road and Lincoln Street interchanges. The Empire Avenue interchange opened in 2019 and the Burbank Boulevard bridge replacement was completed in 2021. The fourth and final phase is in the Santa Clarita Valley, where Caltrans is undergoing construction to extend the carpool lane from the Newhall Pass interchange to Parker Road in Castaic. These lanes are scheduled to open to traffic in 2026. A fifth phase to build a flyover which will connect I-405's carpool lanes with I-5's is in the works, but there are no near plans to construct it. The same plan includes a southerly extension of the HOV lanes to the
San Bernardino Split interchange, but there are no near plans to construct that as well. Widening that segment of the freeway will require several overpass demolitions, as well a major widening through the area, as the freeway is too small to handle the widening. The widening would also result in hundreds of homes and commercial buildings to be demolished. == Exit list ==