California State Route 99 (SR 99), commonly known as Highway 99 or, simply, as 99 (without any further designation), is a north–south state highway in the U.S. state of California, stretching almost the entire length of the Central Valley. From its southern end at I-5 near Wheeler Ridge to its northern end at State Route 36 near Red Bluff, SR 99 goes through the densely-populated eastern parts of the valley. Cities served include Bakersfield, Visalia, Fresno, Madera, Merced, Modesto, Stockton, Sacramento, Yuba City, and Chico.

Almost all of SR 99 south of Sacramento is a freeway, and there are plans to complete this part to Interstate Highway standards, as a parallel route to I-5 for Los Angeles–Sacramento traffic. North of Sacramento, the road ranges from a rural two-lane road to a four-lane freeway.

This route is part of the California Freeway and Expressway System.

From its southern terminus at I-5 in Wheeler Ridge (Wheeler Ridge Interchange) to Sacramento, Route 99 passes through the major cities of the San Joaquin Valley, including Bakersfield, Tulare, Visalia, Fresno, Madera, Merced, Modesto, and Stockton. A majority of this segment is built to freeway standards, However, there are portions that are a four-lane divided highway, including the section near Merced that has two at-grade intersections. The portion of the highway between Fresno and Modesto has been designation the "100th Infantry Battalion Memorial Highway."

The freeway sections connect and serve the numerous small cities—and large urban centers as well—that mostly support the agriculture and industry of the California Central Valley. These segments provide a fast medium-distance haulage route connecting agricultural production with related processing and packing businesses. Most of the freeway also parallels the Union Pacific's Fresno Subdivision. Cars and trucks could sometimes pace the train or follow it when going to Bakersfield or Sacramento.

In Sacramento, Highway 99 first joins with Interstate 80 Business as part of the Capital City Freeway, then runs concurrent with I-5. These SR 99 concurrences are not officially designated by Caltrans, but mapmakers often show it as such. SR 99 signage had existed along that route for motorists' convenience, but was removed in 2000, and replaced by TO SR 99 signs instead.

Highway 99 then splits from I-5 in Northern Sacramento, and then heads along the eastern segment of the Sacramento Valley through Yuba City, and Chico to its northern terminus at Route 36 near Red Bluff. Most of Highway 99 from Sacramento to Red Bluff is a two-lane highway, except for the parts in Yuba City and Chico that are built to freeway standards. The portion between Salida and Manteca is designated the "442nd Regimental Combat Team Memorial Highway."

The first state highway bond issue, approved by the state's voters in 1910, included a north–south highway through the central part of the state consisting of Route 3 through the Sacramento Valley from the Oregon state line south to Sacramento, replacing the Siskiyou Trail, and Route 4 through the San Joaquin Valley from Sacramento to Los Angeles. In addition, a second route followed the west side of the Sacramento Valley, using Route 7 from Red Bluff south to Davis and the short Route 8 east along the proposed Yolo Causeway to Sacramento. North of Bakersfield these closely paralleled some of the main lines of the Southern Pacific Railroad, including the Fresno Line, East and West Valley lines, Shasta Line and Siskiyou Line.

By 1920 paving of both routes from Red Bluff to Los Angeles was completed or in progress, including the only mountain crossing south of Red Bluff, the Ridge Route just north of Los Angeles. To the north of Red Bluff, the road was being graded but not paved over the Siskiyou Mountains into Oregon. Paving was finally completed in mid-1933, when a new alignment (now SR 263) opened through the Shasta River Canyon.

The route from Davis to Oregon via Routes 7 and 3 came to be known as part of the Pacific Highway, an auto trail organized in 1910 to connect Canada and Mexico. The split in the Sacramento Valley was known as the East and West Side highways (the latter also carrying the Pacific Highway). South of Sacramento Route 4 was the Valley Route, but the San Joaquin Valley Tourist and Travel Association held a contest to rename it, selecting Golden State Highway as the winning entry in July 1927.

This north–south central highway became part of U.S. Route 99 in 1926, as part of the new U.S. Highway system developed by the American Association of State Highway Officials (AASHO), though signs were not posted in California until 1928. US 99 also continued southeast from Los Angeles along a paved state highway, Route 9 and 26, to US 80 in El Centro. The paved county road south from El Centro to the Mexican border became a state highway in mid-1931, and part of US 99 in mid-1932.

In mid-1929, AASHO approved a split designation between Sacramento and Red Bluff, with US 99W replacing the original western route via Davis, and US 99E following the East Side Highway (Route 3) via Roseville. A short-lived split also existed between Manteca and Stockton in the early 1930s, with US 99E becoming the main route and US 99W becoming an extended SR 120 where not concurrent with US 50.[citation needed]

A third highway heading north from Sacramento was constructed by the Natomas Company in the 1910s for 13 miles (21 km) along the Sacramento River levee in order to provide access to land reclaimed and sold by the company. Sacramento and Sutter counties continued the road alongside the Sacramento River and Feather River to Nicolaus, where an existing county road crossed the river on a drawbridge and ran north to the East Side Highway at Yuba City. This continuous roadway between Sacramento and Yuba City was dedicated in October 1924 as the Garden Highway.

Parts of the present SR 99 alignment between Sacramento and Yuba City were added to the state highway system in 1933, when the legislature added Route 87 (Sign Route 24, later U.S. Route 40 Alternate) from Woodland north past Yuba City to northwest of Oroville, and in 1949, with the creation of Route 232 (later Sign Route 24) between Sacramento and Marysville. The final piece became Route 245 (no signed number) in 1959, connecting Route 232 near Catlett with Route 87 near Tudor, and following the old Garden Highway across the Feather River to a point east of Tudor. Despite this combined route connecting the same cities as the Garden Highway, the only other piece of the old county road taken for the state highway was a short segment just north of Sacramento, carrying Route 232 between Jibboom Street and El Centro Road.

The implementation of the Interstate Highway System and the mid-1964 state highway renumbering ultimately sealed the fate of the federal designation of Route 99. The Interstates eventually replaced portions of Route 99, causing it to be truncated at both of its ends. Since the remnant did not cross state lines, it was not allowed to keep its federal highway status.[citation needed]

When the Interstate System was being planned in the 1950s, there were two proposals on which way to route the Interstate through the San Joaquin Valley. One was to upgrade U.S. Route 99 to Interstate standards. The other alternative to build the proposed Westside Freeway, which would bypass all the Central Valley communities and thus provide a faster and more direct north-south route through the state. The latter route, which eventually became Interstate 5, was ultimately chosen.

Route 99 was also truncated to Los Angeles, with the old route south to Mexico becoming mainly Interstate 10 and State Route 86. At the same time Route 99 was defined legislatively to run from I-5 near Wheeler Ridge to Red Bluff, but it was only marked as State Route 99 between Sacramento and Yuba City, since the remainder was still US 99 or US 99E. The south end of US 99 was moved further north to Sacramento in late 1966 and SR 99 was extended to Wheeler Ridge; the rest of former US 99 to Los Angeles was either I-5 or the locally maintained San Fernando Road. Several years later US 99 and its branches were removed altogether from California, making SR 99 signage match the legislative definition; all of US 99W, and US 99 north of Red Bluff, remained as other routes (I-80, SR 113, and I-5), while US 99E between Roseville and Marysville became SR 65.[citation needed]

By 1968, all US 99 signs were removed or replaced with SR 99 signs following the completion of I-5. Many of the older highway signs in the southbound lanes of SR 99 still display a control city of Los Angeles, even though SR 99 no longer runs through that city. Caltrans also patched the US 99 shield with the SR 99 shield in many of the highway signs. The most prominent example is the Atwater exit in either direction, on which is clearly visible the old US shield outline underneath the newer spade. Other, better-covered examples are in Tulare (J Street exit) and Merced, where one has to look carefully to note the square green patch.[original research?]

The current long-term goal is to upgrade Route 99 into a six-lane freeway (three in each direction) from Wheeler Ridge to Sacramento. Work to widen Route 99 between Selma and Kingsburg from four to six lanes began on December 21, 2005 and was completed in late 2007. In late 2007 a project began to upgrade an expressway stretch north of Madera to freeway status. From 2010, Route 99 will be widened from four to six lanes from Kingsburg to Goshen. In 2012, this will extend southward from Goshen to Tulare.

Highway 99 is commonly called "The Main Street of California."[citation needed]

It is mentioned in John Steinbeck's The Grapes of Wrath as the main road used by the Joad family during their travels through California.

The 5-mile (8.0 km) segment of Route 99 south of its intersection with Route 70 in Sutter County is named the Bernie Richter Memorial Highway.

The part of State Highway Route 99 consisting of the four-lane expressway between the Edgar Slough south of Chico (Bridge No. 12128) and the Pentz Road overcrossing (Postmile 24.2) is officially designated as the Ray E. Johnson Expressway.

Recently, it has been recommended that Route 99 be upgraded to Interstate Highway standards between its southern end and Stockton (or Sacramento), which would require upgrading some substandard sections and eliminating the last at-grade intersections. Caltrans has recommended Interstate 9 as the designation of the route, although Interstate 7 is a possibility, given the route's proximity to Interstate 5.

Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, and do not necessarily reflect current mileage. The numbers reset at county lines; the start and end postmiles in each county are given in the county column.

Tule fog