▁the ▁total ▁cost ▁will ▁be ▁$ 1 . 0 8 ▁billion . ▁The ▁total ▁cost ▁en comp ass es ▁all ▁six ▁optional ▁elements , ▁including ▁can op ies ▁and ▁additional ▁elev ators ▁at ▁stations , ▁public ▁art , ▁a ▁full - size ▁vehicle ▁maintenance ▁facility , ▁and ▁the ▁full ▁extension ▁of ▁the ▁Som er ville ▁Community ▁Path ▁to ▁Cambridge , ▁but ▁at ▁a ▁nar ro wer , ▁ 1 0 - foot , ▁width .. ▁The ▁new ▁line ▁is ▁expected ▁to ▁be ▁completed ▁at ▁the ▁end ▁of ▁ 2 0 2 1 , ▁with ▁some ▁stations ▁possibly ▁opening ▁that ▁summer . ▁ ▁On ▁December ▁ 2 1 , ▁ 2 0 1 8 , ▁the ▁first ▁of ▁ 2 4 ▁new ▁Green ▁Line ▁vehicles , ▁purchased ▁as ▁part ▁of ▁the ▁GL X ▁project , ▁went ▁into ▁regular ▁passenger ▁service . ▁The ▁shell s ▁and ▁frames ▁for ▁the ▁low - floor ▁C AF ▁cars ▁are ▁fabric ated ▁in ▁Spain , ▁with ▁final ▁assembly ▁in ▁El mi ra , ▁NY . ▁ ▁Crit ic ism ▁ ▁Term inus ▁location ▁ ▁In ▁ 2 0 0 8 , ▁the ▁E PA ▁rat ified ▁the ▁Massachusetts ▁State ▁Im plementation ▁Plan ▁( SI P ) ▁to ▁include ▁an ▁am end ment ▁to ▁the ▁ 1 9 9 4 ▁agreement ▁that ▁subst it uted ▁the ▁planned ▁" the ▁Green ▁Line ▁extension ▁to ▁Ball ▁Square / Tu ft s ▁University " ▁with ▁an ▁" extension ▁to ▁Med ford ▁Hill side ... [ and ] ▁sp ur ▁to ▁Union ▁Square ".