All of SR 198 was added to the state highway system in the three
bond issues floated to pay for the construction of the system. The first bond issue, approved by the state's voters in 1910, included the road from
Visalia west to
Hanford, connecting the two
county seats with the central north–south highway (
Route 4, now
SR 99). As part of the 1916 bond issue, the route was extended west from Hanford through
Coalinga to the coast trunk highway (
Route 2, now
US 101) near
San Lucas, and assigned it the Route 10 designation. The third bond issue, passed in 1919, included a further extension east from Visalia to
Sequoia National Park. The entire length of Route 10 was marked as Sign Route 198 in 1934. This number was adopted legislatively in the
1964 renumbering. The portion east of
Interstate 5 near Coalinga was added to the
California Freeway and Expressway System in 1959, and parts of it have been built as such. As early as 1938, Visalia identified the need for a highway through the city. Due to congestion along SR 198 through Visalia, the California Highway Commission announced in June 1950 plans to convert Mineral King Avenue into a
limited-access freeway. After objection from the Visalia city council over the width of the
right-of-way, the state temporarily halted its plans. In December 1950, the California Highway Commission condemned a
Safeway store under construction in the proposed right-of-way, signaling that the state was continuing with its plans despite the city's objections. Over the next few years, the state continued acquiring property in the city. By 1956, the condemnations had affected roughly 180 people. In October 1956, the California legislature approved $1.1 million toward building a four-lane divided highway way along SR 198, beginning with a portion connecting SR 99 with downtown Visalia. The legislature also approved funding toward acquiring the right of way for extending the highway east of Visalia toward Farmersville. The projected cost in 1958 of the entire freeway east of Visalia was $13 million, and was scheduled to be completed by 1964. As construction of the new highway began, Visalia residents protested the removal of oak trees for the project; as a result, the plans were adjusted to avoid cutting down the trees. On May 29, 1958, the first portion of the freeway opened. In May 1959, the California Division of Highways announced a plan to rebuild of SR 198 in eastern Tulare County; the older roadway would be submerged under the
Terminus Dam, which was later finished in 1962. In July 1959, the state announced plans to build a freeway through Hanford. Later that year in November, state officials announced plans that a portion of the SR 198 freeway in Visalia would be buried in a trench from Mooney Avenue to
Ben Maddox Way, eliminating the need to construct
overpasses. In November 1960, the California legislature authorized $3.4 million toward obtaining right-of-way in both Visalia and Hanford. The relocated roadway around Terminus Dam opened in January 1961. Also that month, the construction of the freeway east of Visalia to Road 192 was approved, with the remainder of the freeway unplanned at that time as contingent on the routing of SR 65. The latter road was originally planned as a freeway along the eastern side of the county, a project that was ultimately canceled. In February 1962, a large rockslide near the Terminus Dam forced drivers to temporarily use the old route, which was not removed after its relocation. In November 1962, California awarded the $1.95 million construction contract to finish the freeway through Visalia. In June 1965, the new freeway from Lemoore to Hanford opened, which was later extended through Hanford in 1967. In July 1965, the new freeway through Visalia opened. The California Division of Highways unveiled plans in September 1969 to rebuild the SR 198 interchange with SR 99. CALTRANS approved the $8.9 million project in 1975, which was completed in 1977. Ahead of the completion in 1972, a portion of SR 198 was expanded to four lanes from the 99 interchange, west to Road 68. Construction began in November 2009 on a project to widen a two-lane, section of SR 198 between SR 43 and SR 99 into a four-lane expressway. The $60 million project was completed in December 2012. ==Future==