The Massachusetts Bay Transportation Authority (MBTA) operates heavy rail, light rail, and bus transit services
in the Boston metropolitan area collectively referred to as the Rapid Transit or Subway system.
The colored rail trunk lines consist of 3 heavy rail lines (Red, Orange, and Blue), one branched light rail system (Green)
, and a short light rail line (the Ashmont-Mattapan High Speed Line, colored as part of the Red Line).
All except the Ashmont-Mattapan Line operate in tunnels in the downtown area, but no route operates entirely underground.
As a matter of fact, only 26 out of the system's 133 stations are actually underground MBTA subway. Wikipedia The Free Encyclopedia. August 19, 2022more on:--Wikipedia