Green Line A branch

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 Union Square and Oak Square 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.

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 cars were hauled by horses to Central Square, then attached to electric cars from Allston for the remainder of the trip into Boston.

On May 18, 1896, tracks opened from Union Square east along North Beacon Street and Commonwealth Avenue to Kenmore Square, merging with the existing tracks on Beacon Street. On June 13, the western terminal was also extended to just shy of Newton Corner (Nonantum Square). On November 8, 1897, Newton service via Commonwealth Avenue began running into the Tremont Street subway. A lengthy Nonantum Square–City Point route via Allston, Coolidge Corner, and Park Square opened on August 4, 1900. On December 9, 1912, service was extended north to Watertown on the existing Galen Street tracks. During the early part of the 20th century, the line was also used for freight service.

The Boylston Street subway was opened to an incline in Kenmore Square on October 3, 1914, with Watertown service via Brighton Center immediately routed into the new tunnel. The first use of high-capacity center-entrance streetcars on the BERy system was as trailers on the Watertown Line in mid-1915. On February 23, 1922, Oak Square short turns were extended to Watertown in the evening peak hour. The Blandford Street portal, on Commonwealth Avenue west of Kenmore, opened October 23, 1932, marking the last change in the route of the service. In 1941, the line became the first line in Boston to have primary service with the new PCC streetcars, which replaced the Types 4 and 5 cars then in service.

In June 1894, the West End applied for city permission to construct a line on North Beacon Street between Union Square and the Watertown border. The Newtonville and Watertown Street Railway soon secured position to build between Watertown Square and Union Square, with the intention to use the West End tracks to reach downtown Boston. After approval by the Watertown Arsenal (which owned a section of North Beacon Street) in 1896 – despite the objection of the West End – the company constructed the line in 1898.

After further disagreements between its parent company Newton and Boston Street Railway and the BERy about operations, the line opened in 1900. Through service on the line between Watertown and the Tremont Street subway, acting as a branch of the Newton-Brighton line, began on November 18, 1900. The BERy took over the line from the Newton and Boston in 1907. The portion west of Market Street was among the only BERy lines never to be double-tracked.