A soon to be part of Boston's MBTA, the Silver Line will connect downtown Boston, and rest of the MBTA to Logan International Airport. This is apparently only a bus line, though the naming is similar to the Red/Blue/Orange/Green Lines, which are all subway/light rail lines.
I don't quite understand the logic, as there already is an Airport stop on the Blue Line. The other end of the Silver Line is supposed to go through some un-connected part of Boston.
You gotta support any increase in public transportation, though.