Park StThe Red Line is the longest subway line in the T. It is made up of two branches and a High Speed Light Rail Line. Both branches start at the Arlington/Cambridge border at Alewife. They both travel along the line into Somerville, Cambridge, Central Boston, and South Boston. In Dorchester the lines split after the JFK/UMass stop. The A branch travels to Ashmont and is the oldest branch, finished in 1924. At Ashmont you can transfer to the Mattapan High Speed Line which is a high speed light rail line which runs along the border of Boston and Milton, terminating in Mattapan. The second branch, the B branch, splits off after JFK/UMass, skipping Savin Hill, and makes its way to Braintree via Quincy. This branch was started in 1971 and was finally completed in the early 1980s. There is also a C branch which is any train headed towards Alewife from either branch.

The Red Line was originally envisioned as an elevated line, like the old Orange Line, that would go from Harvard Sq in Cambridge to Bowdoin Sq in Boston where it would connect with the Tremont St subway. After it was decided to keep trolley traffic and subway traffic separate in the Tremont St subway, a new plan emerged which had trains running elevated from Harvard Sq to Bowdoin Sq but then diving under Boston Harbor to Maverick Sq in East Boston, but due to disputes between the Boston Transit Commission (created by the state to plan the subway system) and the Boston Elevated Railroad Company (BERy, the corporation building the system) the tunnel under the harbor to East Boston was only built for trolleys. Eventually the tunnel was converted to heavy rail for the Blue Line but the clearances were far too narrow for the larger and wider elevated trains. {….}