The A branch or Watertown Line was a streetcar line in the Boston, Massachusetts, area, operating as a branch of the Massachusetts Bay Transportation Authority Green Line. The line ran from Watertown through Newton Corner, Brighton, and Allston to Kenmore Square, then used the Boylston Street subway and Tremont Street subway to reach Park Street station. Portions of the route were built as horsecar lines between 1858 and 1880. The segment between and was electrified in 1889 as part of the Beacon Street line. By 1896, electric routes ran from Newton Corner (Nonantum Square) to downtown Boston via Brighton and via Watertown. Brighton service was extended to Watertown in 1912. The line was operated until 1969, when it was replaced by MBTA bus route 57, though it remained in service for non-revenue moves to Watertown Yard until 1994. History Formation Construction of the Brighton Horse Railroad, a horse car street railway, began in 1858. The line began at Central Square, Cambridge, and crossed the Charles River on the River Street bridge into Allston. It continued through Union Square along Cambridge Street and Washington Street to Oak Square in the center of Brighton. The line was operated by the Union Street Railway, a holding company for the Cambridge Railroad system. After a dispute with the Boston and Worcester Railroad over the right to cross their tracks, the line opened on November 15, 1858. Service was doubled in April 1878, with cars operating every half hour. In 1880, the company opened a second Brighton–Cambridge line via Market Street and Western Avenue. A planned extension that year from Oak Square to Nonantum Square was not built, though a line from Watertown to Nonantum Square was. In the late 1880s, the West End Street Railway consolidated the horse railroads, including the Cambridge Railroad, under its control. The West End opened its first electric streetcar line on January 3, 1889. The line ran between the Allston Carhouse (just north of Union Square) and Park Square via Harvard Street, Beacon Street, Massachusetts Avenue, and Boylston Street. Electric service was extended to Oak Square on January 13. Electric service between Watertown and Mount Auburn began on December 12, 1893; the line was double-tracked later in the decade. On August 18, 1896, the Western Avenue line was double-tracked and electrified. It was the last line that ran over the West Boston Bridge to be electrified; until then, its