High Quality Content by WIKIPEDIA articles! The "B" Branch, also called the Commonwealth Avenue Branch or Boston College Branch, is a branch of the Massachusetts Bay Transportation Authority Green Line in the Boston, Massachusetts area, along which light rail vehicles run on a surface right-of-way down the middle of Commonwealth Avenue. After going underground via the Blandford Street Incline, the tracks merge with the "C" and "D" Branches into Kenmore station. From there the Boylston Street Subway and Tremont Street Subway carry "B" cars to downtown Boston, with regular service turning around at Government Center as of November 2005.