Arlington & Fairfax Electric Railway Co. - opened in 1891 between Washington and Fairfax. In 1937, interurban trains replaced with Auto Railers, or buses capable of operating on roads or rails. Auto Railers discontinued in 1939. Bus subsidiary Arlington & Fairfax Motor Transportation Co. formed in 1932, sold in 1947 to Washington Virginia & Maryland Coach Co.
Washington Alexandria & Mount Vernon Electric Railway Co. - opened in 1892 between Alexandria and Mount Vernon, extended in 1896 to Washington. Sold in 1930 to Alexandria Barcroft & Washington Transit Co., and replaced with buses in 1932.
Washington & Old Dominion Railway Co. - opened in 1912, electrifying a steam railroad line between Washington and Bluemont, and acquiring Great Falls & Old Dominion Railway Co., which in 1906 had opened a line between Washington and Great Falls. Service to Bluemont abandoned in 1932, and to Great Falls abandoned in 1935.
Alexandria Barcroft & Washington Transit Co. - service began in 1921 on Columbia Pike, operated by Robert Lee May. Service added between Washington and Alexandria in 1924, competing with several bus companies which had began operating a few years earlier. Alexandria Barcroft & Washington Transit Co. name adopted in 1924. In 1930 acquired Washington Alexandria & Mount Vernon Electric Railway Co., and in 1932 replaced interurban trains with buses. Acquired by Washington Metropolitan Area Transit Authority in 1973, primary routes now WMATA routes 1 through 4.
Washington Virginia & Maryland Coach Co. - formed in 1925, acquiring various bus companies which had begun operating in early 1920's. In 1947, acquired Arlington & Fairfax Motor Transportation Co. from former interurban railway company. Acquired by Washington Metropolitan Area Transit Authority in 1973, primary routes now WMATA routes 7 through 29.