The $2.3-billion Green Line Extension is trundling towards completion, with the first station in the long-awaited project set to open this fall in Somerville.
GLX Constructors remains on track to complete the entire 4.7-mile extension between Cambridge and Somerville and Medford by the end of the year, at which point it will turn over the new tracks, trains and other equipment to the Massachusetts Bay Transportation Authority (MBTA).