I-5 was originally created in 1956 as part of the Interstate Highway System, but it was predated by several auto trails and highways built in the early 20th century. The Pacific Highway was built in the 1910s and 1920s by the states of California, Oregon, and Washington, and was later incorporated into U.S. Route 99 (US 99) in 1926. I-5 largely follows the route of US 99, with the exception of portions south of Los Angeles and in the Central Valley of California. The freeway was built in segments between 1956 and 1978, including expressway sections of US 99 that were built earlier to bypass various towns along the route. US 99 was removed in 1972.
I-5 is a major Interstate Highway that spans 1,381 miles (2,223 km) and runs north–south through the West Coast states of California, Oregon, and Washington. It connects several major metropolitan areas as well as agricultural regions, seaports, and freight destinations. The freeway ranges from four lanes in some rural sections to 22 lanes in Orange County, California, where it had been widened and reconstructed.[2]
The freeway then traverses the narrow Grapevine Canyon and descends for 12 miles (19 km) into the San Joaquin Valley.[10] At Wheeler Ridge near the south end of the valley, State Route 99 splits from the freeway to serve Bakersfield and other major cities in the Central Valley, while I-5 stays to the west. Now named the West Side Freeway,[4] I-5 travels northwest along the edge of the Central Valley through farmland and avoids populated areas. The freeway is connected to several of the valley's main cities, including Fresno, Merced, and Modesto, by other highways.[5]
Near Tracy, I-580 splits from I-5 to provide the first of several connections to the San Francisco Bay Area; I-205 northeast of Tracy also provides a connection through I-580. The freeway continues north through Stockton to Sacramento, where it follows the Sacramento River through the southern suburbs and along the edge of downtown. I-5 intersects two transcontinental highways in the Sacramento area: US 50 (and unsigned I-305) south of downtown and I-80 in the northern suburbs. After an unsigned concurrency with State Route 99 in northern Sacramento, the freeway turns west to pass the city's airport and resumes its northwestern path at Woodland. It then intersects I-505, another Bay Area connector, near Dunnigan.[5]
The freeway continues north along the western edge of the Sacramento Valley, passing through farmland and several small towns before reaching the end of the valley at Red Bluff. I-5 then traverses the rugged Shasta Cascade region, passing through Redding and crossing Shasta Lake before beginning its ascent towards Mount Shasta. The freeway follows the Sacramento River upstream to the southwestern slopes of the mountain and turns northwest to reach Weed, where it intersects US 97, a major highway serving the Inland Northwest region. I-5 continues through Yreka in the Shasta Valley and follows the Klamath River into the Siskiyou Mountains, where it crosses into Oregon.[5]
I-5 enters Oregon near Siskiyou Summit, which sits at 4,310 feet (1,310 m) and is the highest point on the highway.[11][12] From the summit, I-5 descends by 2,300 feet (700 m) over 6 miles (9.7 km) at a 6 percent grade to reach the Rogue Valley.[13] The freeway passes through Ashland and Medford, running parallel to Oregon Route 99, and turns west to follow the Rogue River to Grants Pass, where it intersects US 199. I-5 then turns north and crosses a series of passes in the Klamath Mountains to reach the Umpqua Valley, where it follows the South Umpqua River to Roseburg.[5][14]
An extensive section of this highway (over 600 mi (970 km)), from approximately Stockton, California, to Portland, Oregon, follows the track of the Siskiyou Trail.[20] This trail was based on an older network of Native American footpaths connecting the Pacific Northwest with California's Central Valley. By the 1820s, trappers from the Hudson's Bay Company were the first non-Native Americans to use the route of today's I-5 to move between today's Washington state and California. During the second half of the 19th century, mule trains, stagecoaches, and the Central Pacific railroad also followed the route of the Siskiyou Trail.[20] By the early 20th century, pioneering automobile roads were built along the path of the Siskiyou Trail, notably the Pacific Highway. The Pacific Highway ran from British Columbia to San Diego, California, and was the immediate predecessor of much of US 99. The route of US 99 was in turn used as a basis for much of the route of today's I-5.
A major deviation from the old US 99 route is the Westside Freeway portion of I-5 in California's Central Valley. To provide a faster and more direct north–south route through the state, the decision was made to build a new freeway to the west and bypass Fresno, Bakersfield, and the rest of population centers in the area instead of upgrading the existing highway (which was re-designated as part of SR 99).[21]
This re-route through California's Central Valley was the last section of I-5 to be constructed, with the final segment dedicated and opened to traffic near Stockton, California, on October 12, 1979. Representatives from both Canada and Mexico attended the dedication to commemorate the first contiguous freeway connecting the North American countries.[22][23] It cost an estimated $2.3 billion in 1979 dollars (equivalent to $7.79 billion in 2023 dollars)[24] to construct all of I-5.[25]
This direct route also bypasses San Francisco and the rest of the San Francisco Bay Area. Original plans called for a loop Interstate with a directional suffix, I-5W.[21] This route now roughly corresponds to I-580 from I-5 south of Tracy to Oakland, I-80 from Oakland to Vacaville, and I-505 from Vacaville to I-5 near Dunnigan. I-5W and most of the other Interstates around the country with directional suffixes were eventually renumbered or eliminated. Nevertheless, San Francisco is still listed as a control city on northbound I-5 between SR 99 and I-580.
By the early 21st century, sections of I-5 had deteriorated due to a maintenance backlog as well as high traffic volumes. Several bridges in Oregon were reconstructed or repaired to accommodate use by heavy freight vehicles.[2]
On December 18, 2017, an Amtrak train derailed on an overpass crossing I-5 near Tacoma, Washington, and blocked several lanes of traffic.[28]
The I-5 corridor forms part of the West Coast Electric Highway, a partnership between the states of California, Oregon, and Washington to build and maintain a network of charging stations for electric vehicles. The pact was formed in 2009 and the first charging stations—spaced 25 to 50 miles (40 to 80 km) apart—opened in 2011.[29] In 2019, the three states also broke ground on a similar charging network for electric trucks along I-5 called the West Coast Clean Transit Corridor Initiative.[30] The program is a collaboration of nine utilities and two agencies representing municipal utilities, and aims to enable electric freight and delivery trucks to operate along the entire West Coast corridor.[31]
I-5 will have a complete set of auxiliary routes (i.e. 105, 205, 305, 405, 505, 605, 705, 805, 905), with the completion of I-905 in San Diego County. Currently, I-80 and I-90 are the only two Interstates to have complete sets of auxiliary routes.
Several routes, including I-305 and I-505 in Oregon, were planned but left unbuilt due to local opposition.
^Rasmussen, Cecilia (March 8, 1993). "L.A. Scene: The City Then and Now". Los Angeles Times. p. B3. Archived from the original on December 16, 2021. Retrieved December 15, 2021 – via Newspapers.com.
^"Respect the Siskiyou Pass"(PDF). Oregon Department of Transportation. September 2005. Archived(PDF) from the original on March 21, 2018. Retrieved December 17, 2021.
^ abcdWashington State Department of Transportation (2014). Washington State Highways, 2014–2015(PDF) (Map). 1:842,000. Olympia: Washington State Department of Transportation. Retrieved December 17, 2021.