Shawmut Branch Railroad
In 1872, the Old Colony & Newport Railway Corporation built the Shawmut Branch Railroad, a steam railroad, as a connection between the Dorchester and Milton Branch and the main line to Boston. The Dorchester and Milton Branch had been built from Neponset, where it connected to the Old Colony Line to run to Mattapan Square. The new Shawmut Branch led off from the Old Colony at Harrison Square to Fields Corner, Shawmut Station and Ashmont, and the rails continued on to meet the Dorchester and Milton Branch after running through Cedar Grove Cemetery.
Electrification of the Shawmut Branch began at the end of 1926. The line was electrified over the next two years, and the new Shawmut Station opened for service on September 1, 1928. At that time the tunnel was placed over the Shawmut section of the line, previously open to the sky. The “high speed” trolley to Mattapan from Ashmont was not finished as an electrified line until 1929. Part of it was previously known as the “Dorchester and Milton Branch Railroad” as a steam railway and extended from Mattapan to Neponset, where it joined the regular Old Colony Line.