From initial construction to U.S. Route 99 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 had not yet been 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. To this day, "Golden State Highway" is SR 99's default name in areas not given other names by the Legislature, and the name continues from its end at Wheeler Ridge on I-5 as the
Golden State Freeway from there to
downtown Los Angeles. 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. A third highway heading north from Sacramento was constructed by the Natomas Company in the 1910s for along the
Sacramento River levee 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
US 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.
As a state route When the
Interstate Highway System was being planned in the 1950s, there were two proposals as to which way to route a freeway through the San Joaquin Valley. One was to upgrade US 99 to Interstate standards. The other proposed alternative was the West Side 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 was eventually chosen and ultimately became Interstate 5. The implementation of the Interstate Highway System and the mid-
1964 state highway renumbering ultimately sealed the fate of the U.S. Highway designation on US 99. The Interstates eventually replaced portions of US 99, causing it to be truncated at both of its ends. US 99 was truncated to Los Angeles, with the old route south to Mexico becoming mainly
I-10 and
SR 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 SR 99 between Sacramento and Yuba City, since the remainder was still US 99 or US 99E. 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. By 1968, all US 99 signs were removed or replaced with SR 99 signs following the completion of I-5. During the 20th century, Caltrans gradually widened Route 99 into a four-lane expressway for the length of the entire segment from Wheeler Ridge to Sacramento. The agency did not immediately upgrade Route 99 to a freeway, since the West Side Freeway had already been selected as the preferred alternative for north–south long-distance traffic. As traffic levels along the Route 99 corridor continued to increase, the at-grade intersections on the expressway became extremely dangerous. Drivers on cross-streets who needed to cross the expressway often had to wait for many minutes at those intersections to find suitable gaps in which to dart across heavy through traffic on Route 99 moving at near-freeway speeds. If drivers became impatient or mistimed the speed of through traffic, the result was often a dangerous
side collision. Therefore, Caltrans upgraded or replaced those intersections one-by-one with freeway interchanges, and often added frontage roads for access to adjacent parcels. This work proceeded very slowly over several decades, as Caltrans needed to balance the rising level of danger at the rural intersections on Route 99 with other urgent construction priorities in California's rapidly growing metropolitan areas. By 2012, there was only one remaining expressway segment with at-grade intersections on Route 99 between Sacramento and Wheeler Ridge, in Merced County between the cities of Chowchilla and Atwater. On December 11, 2012, Caltrans commenced construction on a project to upgrade that segment to a six-lane freeway with full access control. On January 15, 2016, Caltrans officially opened the Plainsburg Road interchange, which completed the conversion of Route 99 south of Sacramento to a freeway built to near-interstate standards. ==Future==