The Camden Line is a MARC commuter rail line that runs for 39 mi (63 km) between Union Station, Washington, D.C., and Camden Station, Baltimore, Maryland, over the CSX Capital Subdivision, and Baltimore Terminal Subdivision. It is one of the oldest commuter lines in the United States still in operation. The Baltimore & Ohio Railroad began running commuter service from Baltimore to Ellicott City over part of the current line's trackage on May 24, 1830, and the line was extended to Washington on August 25, 1835. The Camden Line is the shortest MARC line and along with the Brunswick Line, is the successor to commuter services operated by the B&O. As of 2019, the Camden Line is a weekday-only service.