The Great Falls and Old Dominion Railroad (GF&OD) was an interurban trolley line that ran in Northern Virginia during the early 20th century.
Chartered in 1900 by a group of local landowners and acquired in 1902 by John Roll McLean (owner of The Washington Post) and Senator Stephen Benton Elkins, the 15-mile electrified railroad began operating from Georgetown in Washington, D.C. in 1906. The first scheduled car reached Great Falls Park in Fairfax County, Virginia on July 3 of that year.
From Georgetown, the railroad crossed the Potomac River on a superstructure built on the upstream side of the old Aqueduct Bridge to Rosslyn in Arlington, where it made connections with an older electric trolley line, the Washington, Arlington & Falls Church Railroad. From Rosslyn, the railroad traveled northwest along the north side of Lee Highway (now part of U.S. Route 29) to Cherrydale and then on its own right-of-way (now Old Dominion Drive, Virginia State Route 309) in Arlington and Fairfax Counties through forests, farmland and fruit orchards, bypassing the existing villages of Lewinsville and Langley. At Great Falls, the GF&OD constructed a trolley park, which became a popular destination.