When the line was built in 1872, each railroad had separate tracks and a separate terminal; the current union stations at North Station and South Station had not yet been built. At first, only four connections were provided.
The first connection was from the Old Colony Railroad, the line to Quincy and beyond. That line crossed the Fort Point Channel a bit west of the current bridge, ending with passenger and freight terminals southwest of the current location of South Station (fully south of Kneeland Street). The beginning of the Union Freight Railroad split off the Old Colony Railroad between the bridge and the terminals, heading northeast to Federal Street and then north on Federal Street, a street that ran from the Dorchester Avenue Bridge straight to Dewey Square (the front of South Station).
Continuing north, about 1/3 of the way between Essex Street and Dewey Square, the line was met with a track from the New York and New England Railroad (now the Fairmount Line). This line came over the Fort Point Channel into South Boston (where the South Boston Bypass Road runs now) and back over the channel just south of where the Summer Street Bridge is now, with a passenger depot east of Dewey Square (roughly where the north end of South Station now lies). Freight facilities were in South Boston, where the South Boston Freight Terminal still operates; the Federal Street Freight Depot was later built on the downtown side. The Union Freight Railroad connection split south from the line to the passenger depot just after crossing Fort Point Channel, and ran west to merge with the main line on Federal Street.
The original North Station opened in 1894, lying just west of the old Boston and Maine Railroad northern freight house. The existing connections were kept. A new connection was built between the Union Freight Railroad and the Fitchburg Railroad, east of the old Fitchburg Railroad passenger terminal. Additionally, the track was extended west on Causeway Street to Lowell Street, where it turned north, merging with the original alignment of the Boston and Lowell Railroad and its bridge over the Charles River. This was later simplified, with only the original connection to the Boston and Maine Railroad and the new west connection remaining.
From opening until 1953, UFRR owned its own locomotives. From 1953 until closure in 1970, UFRR leased locomotives from the parent New Haven Railroad.[1]
Edson, William D. Railroad Names: A Directory of Common Carrier Railroads Operating in the United States 1826-1997. 4th edition. Potomac, MD: William D. Edson, 1999. ISBN978-0-9632913-2-5