The Upland–San Bernardino Line was an interurban line operated by the Pacific Electric Railway between Downtown Los Angeles and San Bernardino, California. This line also had shorter service that terminated before the end of the line at Baldwin Park, Covina, and San Dimas. Though service along this line in its entirety was discontinued in November 1941, it stands as the fourth-longest rapid transit line in American history, after the Sacramento Northern Railway's Chico and Colusa services, and the Pacific Electric's own Riverside–Rialto Line.

The Pacific Electric Railway Company, nicknamed the Red Cars, was a privately owned mass transit system in Southern California consisting of electrically powered streetcars, interurban cars, and buses and was the largest electric railway system in the world in the 1920s. Organized around the city centers of Los Angeles and San Bernardino, it connected cities in Los Angeles County, Orange County, San Bernardino County and Riverside County.