[[File:Caltrain JPBX 922 at Santa Clara Station.JPG|thumb|Commuter rail service along the San Francisco Peninsula has been using diesel locomotives ([[EMD F40PH]] pictured above) since the early 1950s; they will be replaced with electric trainsetstrain sets in the 2020s.|alt=An image of Caltrain's current diesel locomotive, an EMD F40PH model.]]
Commuter railroad service on the [[San Francisco Peninsula]] was inaugurated in 1863 as the [[San Francisco and San Jose Rail RoadRailroad]] and purchased by [[Southern Pacific Transportation Company|Southern Pacific]] (SP) in 1870. SP announced that it would investigate the electrification of its line in September 1921, promising better and more frequent service.<ref>{{cite news |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=SU19210907.2.139 |title=Electrifying of S.P. to be investigated |date=September 7, 1921 |newspaper=Sacramento Union |access-date=April 27, 2017 |archive-date=April 28, 2017 |archive-url=https://web.archive.org/web/20170428051758/https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=SU19210907.2.139 |url-status=dead }}</ref> However, SP cited excessive post-war inflation, taxation, and competition from publicly funded highways as factors making electrification neither "practicable or desirable".<ref>{{cite news |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=SU19210917.2.58 |title=Not Practicable to Electrify Lines Down Peninsula—Sproule |date=September 17, 1921 |newspaper=Sacramento Union |access-date=April 27, 2017 |archive-date=April 28, 2017 |archive-url=https://web.archive.org/web/20170428052636/https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&d=SU19210917.2.58 |url-status=dead }}</ref> In the early 1950s, SP began introducing diesel locomotives on the route.<ref>{{cite web|url=http://www.caltrain.com/about/Caltrain150/Milestones/Early_Milestones.html|title=Early Milestones|publisher=Caltrain|access-date=March 29, 2017}}</ref> By 1977, Southern Pacific were facing rapidly declining ridership and petitioned the state [[California Public Utilities Commission|Public Utilities Commission]] to allow them to discontinue the commuter rail operation. From 1980 until 1992, the [[California Department of Transportation]] (Caltrans) and the three service counties, [[San Francisco]], [[San Mateo County, California|San Mateo]], and [[Santa Clara County, California|Santa Clara]], subsidized Southern Pacific operations on the railway until the local Peninsula Corridor Joint Powers Board (PCJPB) acquired the right-of-way in 1991.<ref>{{cite web|url=http://www.caltrain.com/about/Caltrain150/Milestones.html|title=Historic Milestones|publisher=Caltrain|access-date=March 29, 2017}}</ref>
