Although segments of Route 4 had been part of the state highway system since 1909, Route 4 was officially designated as such between US Route 40 (now Interstate 80) and State Route 99 in 1934. Prior to that date, the then-existing segment was officially known as the "Borden Highway", and the bridge over the
San Joaquin River is still referred to as the "Borden Highway Bridge" in tidal tables. Construction of Route 4 did not finish until 1935, however. displacing what was once the largest population of
Filipinos outside of the Philippines. The freeway, while not yet designated SR 4, was initially constructed from a long-term temporary west end at Fresno Avenue, past I-5, up to a temporary east end at Stanislaus Street, essentially becoming a "freeway to nowhere." In 1993, construction of the Crosstown Freeway from Stanislaus Street to SR 99 was finally completed. It is officially the
Ort J. Lofthus Freeway for which it is named after the local civic leader lobbied to get construction of the freeway finished. SR 4, which originally was routed on Charter Way (now Dr. Martin Luther King Jr. Boulevard) and portions of Mariposa and Farmington Roads, transferred its designation onto the Crosstown between I-5 and SR 99. In December 2016, the Crosstown Freeway west of I-5 (though technically not part of SR 4) was extended to Navy Drive via a viaduct bypassing the Boggs Tract neighborhood in Stockton. The connection to Fresno Avenue was subsequently closed to traffic permanently. This was to alleviate heavy traffic to and from the
Port of Stockton that plagued the Boggs Tract neighborhood for several decades. Despite being in the planning books for decades, it is unclear if the Crosstown Freeway past Navy Drive will ever be extended to SR 4 west of Stockton. From 1998 to 2009, a road built by the State Route 4 Bypass Authority, named the State Route 4 Bypass, opened in three phases, bypassing Route 4 in Oakley and Brentwood to the south and west. Many of the signs and local maps designated this extension as simply "Bypass Road". A section of Marsh Creek Road was widened to serve as the connection between the bypass built by the authority and the original Route 4 towards Stockton. In 2012, Caltrans handed over authority for State Route 4 in Oakley and Brentwood to the respective cities. In return, it gained control of the bypass and the upgraded section of Marsh Creek Road, which officially became State Route 4. In 2004, voters passed a half cent tax increase to fund widening from 4 to 8 lanes from Loveridge Road to SR 160. The project lasted from 2010 to 2016 through Pittsburg and Antioch, with the final configuration as three mixed use lanes and one High Occupancy Vehicle (HOV) lane in each direction and auxiliary lanes between interchanges as far as the interchange with SR 160. The median accommodates the
eBART extension of the
Bay Area Rapid Transit (BART) system. In early March 2016, reconfiguration of the interchange of SR 4 and SR 160 was officially opened, allowing westbound SR 4 traffic to access northbound SR 160 directly and southbound SR 160 to access eastbound SR 4. From SR 160 to the Balfour Road interchange, it continues as a four-lane freeway. In 2011, Caltrans awarded $25 million toward upgrading the section from Lone Tree Way to Sand Creek Road to a full freeway and constructing an interchange at Sand Creek Road. Sand Creek interchange opened in 2015 and Balfour Road in 2018. The portion from Balfour Road to
Vasco Road is single-lane each way and has a signal-controlled grade crossing at Marsh Creek Road. The freeway segment of SR 4 in Stockton is part of a proposed route to upgrade SR 99 into
I-7 or
I-9. Under one proposal, the new interstate would go along SR 99 from the split with I-5 at
Wheeler Ridge north through
Fresno to Stockton, where the proposed route would then turn west via the SR 4 freeway to a terminus at I-5. In 2016, Pittsburg moved to install surveillance cameras along their portion of the route, in response to a series of 20 freeway shootings in the area that had taken the lives of six people, and injured 11, in the past year. ==Major intersections==