As mentioned, Braintree–Cohasset was briefly electrified. Overhead electrification on the connecting Nantasket Beach Railroad was more successful, lasting from 1895 to 1932.
The Lower Falls Branch was electrified from 1900 to 1930, when the M&B stopped running streetcars, taking away the line's power source.
G&U was electrified in 1901-02 (except for the 1898-built Upton Loop, which had streetcar service before 1901). Service was operated by Milford & Uxbridge Street Railway cars until 1928; steam passenger service never resumed. Electric freight service lasted until 1946.
The Boston, Revere Beach and Lynn electrified in 1928, offering frequent electric service until 1940.
The Providence, Warren and Bristol electrified in 1902, with EMU service until 1937.
The Attleborough Branch Railroad was converted to a streetcar line in 1903 and ran until about 1930. Similarly, the Worcester & Shrewsbury Railroad was converted in 1900 and run until 1930; from 1903 to 1925, it was the Worcester entry for the Boston and Worcester Street Railway. There have, of course, been numerous similar conversions as parts of the Boston rapid transit network.
The Hoosac Tunnel was electrified from 1911 to 1946 for both freight and passenger trains. Aside from the G&U and the freight/express services on street railways, there were several electric industrial/switching lines. These included the Whitins Machine Works (also operated streetcars), Amesbury Industrial Railway (which operated partially over existing streetcar tracks), Joe Cushing Railroad (Fitchburg), and the Salem Terminal Company.
There were several never-realized electrification plans over the years. South Station, Back Bay station, and the Readville Shops (particularly the powerhouse) were all explicitly designed to support electric suburban service, which was to initially be
on the Dedham loop. Electrification of Boston to Dedham and Providence was studied in 1913, and
an electrified East Boston tunnel was proposed in 1911. The B&A also studied electrification to South Framingham, including the Highland Branch, in 1911.
Harbor tunnel
B&A
Readville