there are currently 5 lines in the mrt system, where they are connected by special stops called interchanges. the lines are north south line, east west line, north east line, circle line and downtown line. the circle line opened in four stages from 28 may 2009 to 14 january 2012. stage 1 of downtown line opened on 22 december 2013 with its official opening made on 21 december 2013 by prime minister lee hsien loong.