On August 15, 1896, the Boston Elevated Railway (BERy) added tracks on newly constructed Commonwealth Avenue from the Newton town line east to Chestnut Hill Avenue, where they were connected to the existing Beacon Street Line at Cleveland Circle.
Except for rights to the Watertown Line inherited from the West End Street Railway, the BERy did not have operating rights in Newton.
Instead, the Commonwealth Avenue Street Railway was built westward on the wide median of Commonwealth Avenue to Auburndale in 1895.
It was soon taken over and operated by the Middlesex and Boston Street Railway (M&B).
The two lines met at Lake Street station on the town line.

BERy cars from Lake Street began running into the Tremont Street subway via Beacon Street when the subway opened on September 1, 1897.
On May 26, 1900, tracks on Commonwealth Avenue were completed from Chestnut Hill Avenue to Packards Corner, at which point Lake Street became the terminus of the Commonwealth Avenue line, which also ran into the subway.
Except for occasional service disruptions due to track work or blockages on Commonwealth Avenue, Boston College has been the terminus of the Commonwealth Avenue line (B branch) since 1900.
On August 15, 1896, the Boston Elevated Railway (BERy) added tracks on newly constructed Commonwealth Avenue from the Newton town line east to Chestnut Hill Avenue, where they were connected to the existing Beacon Street Line at Cleveland Circle. Except for rights to the Watertown Line inherited from the West End Street Railway, the BERy did not have operating rights in Newton. Instead, the Commonwealth Avenue Street Railway was built westward on the wide median of Commonwealth Avenue to Auburndale in 1895. It was soon taken over and operated by the Middlesex and Boston Street Railway (M&B). The two lines met at Lake Street station on the town line.
BERy cars from Lake Street began running into the Tremont Street subway via Beacon Street when the subway opened on September 1, 1897. On May 26, 1900, tracks on Commonwealth Avenue were completed from Chestnut Hill Avenue to Packards Corner, at which point Lake Street became the terminus of the Commonwealth Avenue line, which also ran into the subway. Except for occasional service disruptions due to track work or blockages on Commonwealth Avenue, Boston College has been the terminus of the Commonwealth Avenue line (B branch) since 1900.
Boston College station