Interest in building a new rail line from Washington to points west was initially generated by businessmen in Washington and Montgomery County, Maryland. In 1853 they obtained a corporate charter from the Maryland General Assembly to form the Metropolitan Railroad. The proposed line would run from Washington to the vicinity of Frederick, Maryland, where it would connect with the B&O main line, and continue to Hagerstown, Maryland. The company conducted some initial land surveys, but had difficulty raising funds and went bankrupt in 1863. Previously the B&O had not been interested in building a new route out of Washington, but following the Metropolitan Railroad's failure, it took over the expired charter in 1865. Construction began in 1866 along a slightly different route, connecting with the main line at Point of Rocks, Maryland. The line opened in 1873 as the B&O's Metropolitan Branch. Upon the opening of the branch on April 30, 1873, the B&O rerouted its through passenger traffic through Washington, and the Old Main Line, from Point of Rocks to Relay, was reduced to secondary status as far as passenger service was concerned. Some through freight trains were also rerouted to use the new line. Due to increasing congestion, the B&O began to add double track portions to the line in 1886. The Washington-to-Gaithersburg section was double-tracked by 1893. During the peak years of passenger operation, 1893 to the 1920s, there were eighteen trains per day, with as many as 28 stops along the Met Branch. Significant engineering features include bridges across:
The Georgetown Branch ran from a junction north of the Silver Spring station to the Georgetown area of Washington, D.C. The branch was built between 1892 and 1910. It was originally intended to be a B&O extension that would cross the Potomac River near the Chain Bridge. In 1904 the B&O reached agreement with the Pennsylvania Railroad to access the nearby Long Bridge over the Potomac, and then proceeded to use the Georgetown Branch as a spur servicing local industries in Silver Spring, Chevy Chase, Bethesda and Georgetown. Significant engineering features that were built on the branch included the Rock Creek Trestle in Chevy Chase, the Dalecarlia Tunnel and a through-truss bridge over the Chesapeake and Ohio Canal. CSX abandoned the Georgetown Branch in 1986, with the last train running in June 1985, and the spur is now accessible to the public as the Capital Crescent Trail. The Bethesda-to-Silver Spring portion of the spur is also providing a right-of-way for the Purple Linelight rail system, which has been under construction since 2017. The existing Rock Creek trestle was demolished and is being replaced by new bridges to support the light rail tracks and the bicycle trail.
Current operation
Through mergers, the line became part of the CSX system in 1987. CSX organized its Metropolitan Subdivision as a combination of the original B&O Met Branch plus a section of the B&O original main line northwest of Point of Rocks, which had opened in 1834. The entire subdivision is signaled for bi-directional running. There is a spur that services the Dickerson Generating Station at Dickerson, and a trash-transfer facility spur at Derwood. The interlockings on the line are : F Tower, QN Tower, Georgetown Jct, Montrose, Derwood, Cloppers, Buck Lodge, Dickerson, PEPCO, Tuscarora, East Rocks, Point of Rocks, East Brunswick, WB Tower and Weverton.
